'Items' can mean words and definitions, as well as phrases, but can also mean pictures of different kinds of leaves together with the names of the trees that they come from; or audio files of pieces of music together with the genre of music, the name of the performer and the name of song.
When you add an individual 'item' to a course, Memrise will look for it in our central dictionaries and, if it exists, you can choose to add it to your course's database, or you can enter your own. It's important to note that databases are unique to each course. They cannot be shared or reused in other courses. If you enter new sets of items, or modify the ones that were pre-existent, they will not affect nor be added to our central dictionaries.
The settings of what is displayed and what is tested are done on the levels, not on the database. The database is the store of all of the information about every 'item' in the course. The levels are where those items are arranged by course creators into a learnable format.
Editing a Database
Where can I find the Databases tab?