Many functions can be written as powers series about some point of their domain. About a point a (say) we get
f(a+h)=f(a)+1!1f′(a)h+2!1f′′(a)h2+3!1f′′′(a)h3+...
which we call the Taylor series of f.
The case a=0 is known as the Maclaurin series of f.
The Taylor Series for sin(x) and cos(x) are shown below.