Does 2.5D mean Isometric?
No, it can be done from both types of play.
"2.5D, short for two-and-a-half dimensional, although technically incorrect (the concept is unrelated to modern mathematical ideas of non-integer dimension), is a term that has become popular to describe a number of different phenomena, most of which are related to computing and especially video games."
"One use of the term is to describe a style of graphics in video games with 2D gameplay, but with a limited 3D appearance, popular in the late 1980s and early 1990s. A collection of 2D sprites moves independently of each other, and/or the background, using the theory of parallaxing to create a sense of depth. A number of games also uses the closely related concept of parallax scrolling, which creates a sense of depth between the actual interactive game elements, and the background. Because of this method, the effect only works when the game character is in motion. One good example game using this style is NiGHTS Into Dreams."