These operators are used to find the existence of terms within a document in relation to other terms.
The documents retrieved must contain both the words/phrases you have typed. The terms can appear anywhere in the document (unless modified by additional operators).
The document must contain at least one of the entered words or phrases. Both terms may be present.
The retrieved documents must contain the first term and must not contain the second, no matter where else it appears in the document.
The documents must contain either the first search term or the second, but not both terms.
The retrieved documents must contain the first search term but only if the second term is not in the same paragraph as the first. Both terms can appear in the document; just not in the same paragraph.
The BUTNOT operator is an even more precise form of EXCEPT. The document must contain the first term, and it must not appear as part of the second term. For example, the query "WORLD BUTNOT WORLD BANK" will find documents that contain the word "WORLD", and which may or may not contain "BANK", but will not find "WORLD BANK" where it appears as a phrase. Similarly, "PLAYER BUTNOT MEDIA PLAYER" would find the word "PLAYER", but not where it occurs as part of the phrase "MEDIA PLAYER".