Using AND between search terms in Seeker (and other databases) will narrow your search results. Each new term is an additional requirement that your results need to fulfill.
1. Universities: 77,473,393 results
2. Universities AND Maryland: 778,147 results 
3. Universities AND Maryland AND Loyola: 7,511 results
Using OR between search terms in Seeker (and other databases) will broaden your search results. This can be an efficient way to incorporate synonyms into your search without starting all over, but you need to be careful about HOW you input "OR" into a database.
Do not select "OR" in the drop-down menu between the search fields. Your results will explode and become less relevant. Just trust us.
Instead, put "OR" in the same search box with synonyms so that the database knows results could contain one or the other term, but not necessarily both.
In the search below, I'm trying to get items that pertain to illiteracy and then either the terms health or nutrition. In other words, I want my results to be a combination of ("illiteracy and health") and ("illiteracy and nutrition") - but not necessarily a combination of all three terms terms (illiteracy, health, and nutrition).
1. Illiteracy: 39,579 results 
2. Illiteracy AND health: 8,299 results (using AND narrows it down) 
3. Illiteracy AND health OR nutrition: 3,132,952 results (= crazy) 
4. Illiteracy AND (health OR nutrition): 8,461 results (= good) 