database

one word  A set of related files that is created and managed by a database management system (DBMS).

decades

1980s, '90s

dial up, dial out, dial in

verb, two words

dial-up

(as in dial-up connection)  A temporary connection to or between computers made through the telephone network by “dialing up”.

dialup, dialout, dialin

adj. or noun, one word

Double-click

not "double click on"

download

one word; downloadable   To transfer data/files from one device to another.

dpi

dots per inch; e.g., 300dpi, no spaces

drop down

verb; two words

drop-down

adj; menus in DOS and Windows environments; see "pull-down"