What is it?
To be “pragmatic” in everyday discourse is to deal with a particular situation in a practical way.
Merriam Webster: simple definition of pragmatic: dealing with the problems that exist in a specific situation in a reasonable and logical way instead of depending on ideas and theories.
The definition of “pragmatics” in relation to language is not so different.
It refers to language as it is used in daily, social contexts including such things as taking turns in conversation and word and sentence organization to make sense to others.
Children (or adults, come to that) who have difficulties with pragmatics of language often appear to be proficient speakers. They have a good grasp of grammar and vocabulary. Their communication breaks down, however, when they have a range of difficulties in using the language they have to make themselves be clearly understood and make successful connections and friendships.
This article on the website of the American Speech and Hearing Association gives a clear explanation with some good examples of the kinds of communication challenges that are present in a pragmatic language disorder:
There are also some excellent suggestions for how to help someone who has this type of language impairment: