Exactly what is a tick count? Can a tick count be converted to seconds?

In a application a certain event takes place and at the point in time it occurs I save the current tick count. Now later another event takes place. At the point in time of the second event I get the current tick count. What I need to be able to resolve is how many seconds elapsed from the first event to the second event and the only thing I have are the two tick counts. Using Time doesn't work for this situation.