In this paper, we study properties of functions and sequences with a semi-heavy tail, that is, functions and sequences of the form w(x) = e −βx f (x), β > 0, resp., w n = c n f n , 0 < c < 1, where the function f (x), resp., the sequence (f n ), is regularly varying. Among others, we give a representation theorem and study convolution properties. The paper includes several examples and applications in probability theory.