Definition of a thriller

- A thriller is a film which tries to scare the audience but not in the same way as a horror.

A thriller tries to scare you with realistic things such as things that could actually happen. It doesn't focus on trying to make you scared by showing blood and gore like Horror films. A thriller works more on a level of creating suspense for the audience so they don't know what is happening. Sometimes a thriller sets out to confuse you.
In general a thriller is something that plays with your mind more than showing horrific things that are meant to shock and horrify you. It can do that with a more Psychological element to it (like in Psychological Thrillers) rather than having to show you everything. They tend to leave more to the imagination and leave the audience to work out things for themselves, usually revealing all the information at the end. They have a tendency to leave some information out which results in the viewer asking questions and thinking about what they have seen.