BECAUSE IT WAS a small hotel and Hong Kong is forever full of visitors, I broke precedent and reserved. I reserved well ahead. the fringe benefit was plenty of time to ponder this question:

"For exactly what wondrous thing should your little heart throb when the confirmation slip reads, "Rate includes Rediffsion"?

"Don't ask me," said a friend. "I'm still trying to figure out what they mean in Texas by a "twin double.'"

I think the moral of this story is that you can go long and far, but wherever you are you're expected to speak "hotel."

Most travelers eventually learn in the midst of an awkward situation that "hotel-speak" can cost comfort or money. There is, for instance, a monumental difference between "with bath" and "with private bath," though fortunately it is usually only a less-than-the-best places abroad that you need to consider that.

Other things are more perplexing than consequential. Rediffusion turned out to be a piped-in radio service, and in this country a twin-bed double is usually a room with two double-to-king-size beds.

But if you're new to the travel scene or out of touch, what do you need to know? Well, everything changes, but in 1980 I'd say you can get along well enough if you learn certain key words and phrases. For instance:

Best Available. If this is what you're promised in the way of a room, don't think you're set for a sea view or something extra special. It merely means you'll get the best room available when you arrive. It does not mean you've nailed down the best room in the hotel. similarly, when you ask for "best available," that means you'll take anything, but you'd like something upscale and are prepared to pay for it. t

Blocked Space. "Space for that date is blocked" normally translates to "We've promised everything to a bunch of tours and conventions." In fact, though, the exact number of convention delegate and tour participants has been known to change, sometimes daily. Recheck more than once if you truly care, and you may be rewarded.

Check-In Time. Never mind that your plane arrives at 9 a.m. You may not be able to get into your hotel room until 1 or 2 p.m. Yes, a day is a day, except that in hotels it commences at various hours, and you can't count on starting yours until the last tenants finish theirs. Read on.

Check-Out Time. Hotels all post the time at which guests must give up their rooms or pay for another day. Lately, the hour in many places is as early as 11 a.m. You may be allowed tolinger longer if you ask the management. But also ask if there is any charge.

Child. Once upon a time, this meant infant-to-pint-size people. Many hotels now take a stretched-out view and let parents share with babes as big as basketball players -- no charge as long as they share the same room and are 18 years of age or under. A few hotels still decree that "children" must be under 13 for free sharing; some make it under 17. Since the best surprise is sometimes no surprise, check the cut-offs.

Confirmed Reservation. A confirmation is only as good as the paper it's written on, which is to say that an oral understanding, unless you're given a transaction number, has next to no legal worth. Written confirmation may have limits, to; for example, the hotel may not be obligated to give you a room if you arrive "late," after, say, 4 or 6 p.m. That's why you might well ask about "guaranteed reservations" and learn how your hotel defines them.

Day Rate. This can be a good deal iF you can get it, IF you arive somewhere at the crack of dawn and need to sleep, IF your're pushing on later in the day. It's a cheaper rate that's most often available at hotels and motels in the vicinity of airports, between the hours of 6 a.m. and 5 p.m.

Double. Specifically, a room with a double bed. It can also be a room for two or more persons and have two twin (narrow) beds. Best to say what you want.

Double Rate. The per-room charge for rooms big enough for two or more guests. Watch out, though, because sometimes people quote the "double occupancy" rate, meaning the rate for each of two persons sharing.

Full Pension. That's "Angle-European" for three meals a day included in the room rate, often called "American Plan." There are also "Modified American Plan and "Demi-Pension," meaning two meals (breakfast and lunch or dinner) included.

The drift is toward simply "breakfast included" when that's the case. "Continental Plan means rolls-and-beverage breakfast, while "Bermuda Plan" is a rarely used term for full "American" or "English" version with eggs and all the trimmings. "European Plan," on the other hand, means no meal included.

Junior Suite. Not tow or more rooms, but one room with some kind of partition or furniture arrangement separating bedroom and sitting areas.

Lanai. Sometimes means a balcony off the room, but usually means a more or less private terrace.

No-Show. A really rotten type of person who, without calling to cancel, simply fails to show up to claim a reserved room. Annihilation tactics are being developed, and no-shows are sometimes bugged by bills anyhow.

Pension. Principally in Europe, a guesthous or boarding house, though not necessarily one lacking in the major comforts. There's a wide range in prices and amenities, though the majority are simple, "home-style" accommodations with communal bathrooms. You may or may not be required to sign up for meals, but inquire in advance.

Rack Rate. The official rate quoted by the hotel. That doesn't mean they won't reduce a price if they're not enjoying the best of all possible periods, and if you're included to ask. These days one hears of bargaining starting up again in London. There have also been flat-out markdowns in Hawaii this summer.

Service Charge. An amount added to your bill, usually 10 to 15 percent, that's suppose to eliminate the need to tip hotel personnel. In fact, you're often stuck with both duties, but you should nose around and find out what's expected.

Supplement. An expanding area of enterprise. Lately a number of resort hotels, in particular, add extra charges (supplements) in the form of "energy" surcharges." It is therefore more and more a good idea to ask, "Does that rate include taxes, service charges and all supplements?"

Tourist Hotels. Sometimes it seems whim determines both the official and unofficial classification of hotels. For sure, though, a tourist-class hotel will be limited in its amenities. First class generally means "medium," and deluxe is supposed to be "top grade." In other words, you can usually count on deluxe hotels to have all rooms with private baths, as well as high-class restaurants, public rooms, elevators and many services. After that, specify what you're after and ask if it's available.

Is that all? No, but with this basic vocabulary you can safely open communication.