A suffix is a small sub-unit of language. It may be added at the end of any of many other words to indicate a change of meaning or, commonly, to create a related word in a different word class from that to which the original word belongs. For example, the suffix '-ment' creates a noun from a verb: the noun 'judgement' is a record of an act of judging, from the verb 'to judge', and an 'establishment is something that has been established.
Suffixes make one of a small group of bound morphemes which cannot normally be used on their own, but must be attached to other words. Prefixes form another such group. The general name for the whole group is affix. In English, the important affixes are prefixed or suffixed