Semantic (or sometimes called lexical) fields are a technique often used by writers to keep a certain image persistent in their readers' mind.
They are a collection of words which are related to one another be it through their similar meanings, or through a more abstract relation.
For example, if a writer is writing a poem or a novel about a ship, they will surely use words such as ocean, waves, sea, tide, blue, storm, wind, sails, etc.
It is a collection of words which relate to each other in a semantic (which means meaning) or abstract way.
