Temporarily ignoring unwanted memories, thoughts, and feelings until you have time and bandwidth to deal with them properly.
Analogy
Schindler’s List is a fantastic film, but you need to be in a particular kind of mood to watch it. It’s probably not the best thing to watch before a job interview, or a birthday party. So you put it in your “watch later” list and save it for an evening when you have the time and energy to deal with the difficult emotions it will bring up.
Discussion
Suppression and repression are very similar. In fact, they’re pretty much identical except for one thing: Suppression is a conscious decision. You decide not think about your credit card bill when you’re playing with your kids, because you know it will ruin your mood. But you also know you’re going to have to deal with it eventually, and so you schedule some time on Thursday evening to go through the charges and make a payment. And when Thursday evening comes around, you actually do it.
If you repress your thoughts about your credit card bill, they disappear into the storage locker of your mind and only come back again when a collection agency is repossessing your car.
This is why suppression is considered a mature defense. You consciously manage your time and emotions so as to deal with a problem as effectively as possible. This leads to more satisfying outcomes from unpleasant situations, and prevents bad experiences from piling up and starting to rot in the back of your head.