Has definite volume. This means that liquid takes up the same space, no matter where you keep it, in a jug orin a bottle.
A sample of fluid at a specific temperature and pressure has a preferred volume, because its molecules have a least-energy separation distance. Imagine first a line of people queuing for beer: they don't like to leave a gap big enough for someone else to slip in, which makes an 'attractive force', but they don't want to actually touch ('repulsive force') so there is a preferred distance d. A line of N people will be about Nd long.
Now let them spread out on all the available floor space, instead of forming a queue like the English. Gaps will still fill up, to be near the bar, but outside (for instance) a Tokyo metro train, where special employees apply pressure to squeeze more, the people keep their comfortable distance d. If they arrange themselves in a square array, like a crystal, each person is using an area d², so N people will fill up about Nd². A hexagonal array would take about 12% less area, a fluid arrangement takes more, and you need a large number of people for the area to become definite -- with half a dozen people, it's poorly defined, but with millions, the variations average out. A million people will take up an area of about one square kilometre, if they don't need to move around.
For fluid molecules, or people in microgravity*, the same idea works in 3D: they will fill up a fairly well defined volume, roughly Nd³, which can be changed by squeezing them, or making them more active (with heat, or 3D dance music) so they demand a bigger d.
For numerical detail, and exactly how definite the volume is, you need to study statistical physics: but that's the basic idea.