To release hidden stress or pent-up emotions, often to a friend or significant other. Sometimes harmful depending on the way it is released, such as forcefully or angrily, but it can also be released emotionally. Sometimes just talking about the topic helps people vent and be in a bettermood.
"I really need someone to vent to..."
Sometimes, if you can't sleep, you just need to vent.
"Thomas just vented to me and I feel really bad for him"
an ability to share emotions in a time of need. Sometimes venting can leed to your problems onto other people. This is not always the case but you should be careful when unlifting personal feelings..