On Monday, President Obama commuted the sentences of 46 nonviolent drug offenders, part of a bigger effort his administration is making to try to ease such people out of the federal prison system.

The Obama administration said last year it was pushing to free nonviolent offenders who were, in the words of former Attorney General Eric H. Holder Jr., “deserving individuals who do not pose a threat to public safety.” More than 35,000 inmates have applied for early releases under this new initiative, which is taking a while because it involves such a large number of applications and a complex review system.

The idea, emphasized by Obama on Monday, is that the people being freed were sent to prison during a different era, when sentencing guidelines enacted during a crime wave meant that many were ordered to serve prison terms longer than what they would receive today. It also means that many people are now waiting to hear if they are going to receive a presidential commutation, something that has rarely been granted over the years.

Commutations are not the same thing as presidential pardons, which sounds very obvious if you already know this, but just in case anyone out there is curious, here’s a breakdown of how the whole process works.

What a commutation or pardon means

People can apply for executive clemency — meaning pardons and commutations — and these requests go through the Justice Department’s Office of the Pardon Attorney. The applications go through the deputy attorney general’s office before making their way to the White House.

When a sentence is commuted, that does not suggest that the person was innocent, according to the Justice Department. It does cut off a sentence, but it does not do away with what are known as “civil disabilities” — another way of saying that convicted felons can’t sit on federal juries or, in some cases, vote.

A pardon, meanwhile, is something different. When presidents pardon people, they also don’t retroactively say that the person was innocent, but they do take away these civil disabilities. In some states, there are also ways for people can regain the right to vote without getting a presidential pardon, but a presidential pardon is still the only way for felons to be allowed to possess firearms.

An easy way to remember the difference: Pardons are generally granted after someone already served their time, while commutations typically happen when someone is behind bars, according to Families Against Mandatory Minimums (FAMM), a nonprofit group that is participating in efforts to review prisoner applications.

The limits to what a pardon or commutation can do

Presidential pardons, meanwhile, do not expunge records, though criminal histories are supposed to be updated to show that the person was later pardoned.

Generally, pardons can help people when applying for jobs. In some states, pardons expunge the felony conviction from a person’s record, FAMM reports. Illinois allows for some felony convictions to be expunged or sealed, and in certain cases you don’t even need a pardon for that, while Kansas allows people to ask the courts to expunge records as well. (The National Association of Criminal Defense Lawyers has more here.)

There are also limits to what kind of sentence a president can commute. While presidents can commute federal sentences, they cannot grant clemency for any state-level convictions. In those cases, governors or state boards handle the requests, and this varies from state to state. For example, in Georgia, only the state Board of Pardons and Paroles can commute death sentences.

The rarity of presidential commutations

Commutations do not happen very often, and they are much rarer than presidential pardons. The commutations granted Monday more than double the number Obama has issued since taking office.

Before this week, he had granted 43 commutations and 64 pardons. Obama has now commuted more sentences than any president since Lyndon B. Johnson, who commuted 226 sentences during his time in the Oval Office, according to federal statistics.

He has also commuted more sentences than the number granted by his four immediate predecessors — Presidents George W. Bush, Clinton, George H.W. Bush and Reagan.