animal africa^2 savannah
To boost a term use the caret symbol ^ with a boost factor (a number) at the end of the term you are searching. The higher the boost factor, the more relevant the term will be.
The + symbol (also known as the "required" operator) requires that the term after the + symbol exist somewhere in a field in at least one document in order for the query to return a match.
The - symbol or "prohibit" operator excludes documents that contain the term after the - symbol.