Acrylic paint is a fast-drying paint containing pigment suspended in an acrylic polymer resin. Acrylic paints can be diluted with water, but become water-resistant when dry. Depending on how much the paint is diluted (with water), the finished acrylic painting can resemble a watercolor or an oil painting.
Acrylics are sometimes used in place of watercolors because acrylics dry closer to the desired color (slightly darker, usually), while watercolors dry lighter (and often unpredictably, especaially for beginning artists.
Acrylics can also be used as an alternative to oil paint because acrylics dry much faster than oil paints. Oil paints, which consist of pigment suspended in an oil (usually linseed, or other natural oil) base, can take a very long time to dry. Acrylic paints can achieve an oil-paint-like effect, and do so in much less time. Applied to look like oil paints, acrylics are somewhat limited due to the superior color range of oil paints, and the fact that acrylic paints dry to a shiny, smooth (some say 'cartoonish') effect--not surprising since acrylic paints are, basically, plastic.
Acrylics do have the ability to bond to many diverse surfaces.
Acrylic paintings, ideally, should be treated as if they are as different from oil painting as watercolor is different from oil painting. There are techniques which are available only to acrylic painters, and there are also restrictions which are unique to acrylic painting. Therefore, likening an acrylic painting to an oil painting (or to a watercolour painting) is a false comparison.
Acrylic paint can be removed with turpintine, mineral spirits (also known as white spirits), ammonia, and rubbing alcohol.