Filenames can include a space; however, this can cause complications if you’re running programs from the command line because a program named interview notes would be viewed as a command to run two files: interview and notes. To avoid confusion, the two words can be enclosed in quotes: “interview notes.” (This is important when using Linux in terminal mode by way of its command interpretive shell. From a Linux desktop GUI, users choose names from a list so there’s seldom a need to type the filename.)