Series

Series[f,{x,x0,n}] generates a power series expansion for f about the point x=x0 to order (x-x0)n, where n is an explicit integer. 

Series[f,x->x0] generates the leading term of a power series expansion for f about the point x=x0. 

Series[f,{x,x0,nx},{y,y0,ny},…] successively finds series expansions with respect to x, then y, etc. 

Please visit the official Wolfram Language Reference for more details and examples on core symbols.