What is a group of letters placed after a word to change its meaning called?

A group of letters placed after a word to change its meaning is specifically called a suffix. Suffixes are added to the end of root words to alter their meanings or grammatical function. For example, adding "-ing" to the verb "play" transforms it into "playing," indicating an ongoing action.

While terms such as infix, prefix, and affix are related to modifications of words, they have specific definitions that differ from that of a suffix. An infix is inserted within a word, a prefix is a group of letters added at the beginning of a word, and the term affix can refer to both prefixes and suffixes as a general category of word modifications. However, in the context of the question focusing specifically on letters that appear at the end of words, suffix encapsulates this meaning accurately.