What is the difference between a full search and a screening search?

Screening Searches are searches that are conducted to quickly check the availability of a proposed mark(s) and to eliminate any proposed marks that are in direct conflict with any existing mark(s)
Full searches are searches covering all possible marks that a proposed mark might conflict with (on grounds of being confusing and/or misleading) during the course of the registration process and/or while the trademark is used in the market.