Let T be a rooted tree with n nodes.
In the general case, let T be the subgroup of diagonal matrices.
Let T be the "time" whose axis has length continuum.
Let T be a regular chain in the polynomial ring R.
Let T be the year's last two digits.
Let T be the first time k copies of each coupon are collected.
Let T be a set consisting of all infinite sequences of 0s and 1s.
For example, let T be a torus, as shown on the right.
Let T be the number of different types of parts.
Let T be the time to access the memory.