I saw a question saying that the coefficient of thermal expansion of a liquid is (alpha). I was confused that (alpha) is what? The coefficient of linear expansion or volume expansion. And from there I thought that is the linear coefficient for liquids defined? So i just want to know, How many types of thermal expansion are there in liquids?
The specific coefficient of thermal expansion being discussed in the literature should be specified or at least implied. The coefficient of volumetric thermal expansion is 3x the coefficient of linear expansion. In the case of linear expansion of a liquid, the initial and final shapes must be constrained to be geometrically similar, and the pressure on the liquid must be the same. These requirements mean that, for all practical purposes, the answer given by @Bhavya Sharma is correct.