What does the term phase actually mean?
I think wikipedia can more than adequately answer your question. 

http://en.wikipedia.org/wiki/Phase_(waves)

However, in brief, the phase term describes the relationship between a waveform and a fixed reference point in time. For example the sinusoid $sin(\omega t)$ is zero at $t = 0$ whereas $sin(\omega t - \phi)$ is zero at $t = \phi$. $\phi$ could be referred to here as the phase offset.