experience is the knowledge and skill gained through doing something for a period of time, the things that have happened to a person that influence the way they think and behave, and an event or activity that affects someone.
The Oxford Learner's Dictionary sorts the noun's senses by grammar. Two are uncountable: knowledge and skill gained through doing something over time, and the process of gaining it, as in "We all learn by experience"; and the things that have happened to you that influence the way you think and behave, as in "Experience has taught me that life can be very unfair." Oxford lists the pattern in somebody's experience under this second sense; see 📝In my experience.
As a countable noun, an experience is an event or activity that affects you in some way. A singular sense, often in compounds, means what it is like for somebody to use a service, do an activity or attend an event, as in customer experience or 📝user experience. Another singular sense, the… experience, names events or knowledge shared by all the members of a particular group in society that influence the way they think and behave.
As a verb, to experience something is to have a particular situation affect you or happen to you, or to have and be aware of a particular emotion or physical feeling. The word dates from late Middle English, via Old French from Latin experientia, from experiri, "try"; Oxford compares experiment and expert.
See: 📝The Felt Presence of Direct Experience