In Yogic philosophy, a Samskara is a behavior inherited from a past life that will be repeated in this life. A modern definition might be bringing reactions based on childhood experiences—a previous time that could be viewed as a “past life”—into the present.
For example, say you have a boss who reminds you very much of one of your parents. Your reactions toward your boss might be more aligned with a parent/child relationship than a professional, business connection. (You can see how that might be a little weird.)
At their most serious, Samskaras are repeating cycles of negative behavior that bewilder us. We try to break free, but we don’t seem to be able to. You could draw a parallel between Samskaras and addiction, though there are a lot of mitigating factors, such as physical dependency, that come into that picture.
In a more general sense, Samskaras pertain to emotional behaviors, like the inability to stop texting an ex. But Samskaras aren’t horrible negative things we’re doomed to endure until our next life. When reframed as teachers with good lessons we can learn, they become a valuable part of our spiritual lives.
For exercises on learning and breaking free from Samskaras, see Day 19 of Yoga Mind: Journey Beyond the Physical.