What does 'theta' mean in statistics?

In statistics, θ, the lowercase Greek letter 'theta', is the usual name for a (vector of) parameter(s) of some general probability distribution. A common problem is to find the value(s) of theta. Notice that there isn't any meaning in naming a parameter this way. We might as well call it anything else. In fact, a lot of distributions have parameters which are usually given other names. For example, it is common use to name the the mean and deviation of the normal distribution μ (read: 'mu') and deviation σ ('sigma'), respectively.