l (lowercase L) command in bash terminal

l is probably an alias for something like ls -F. The -F option causes ls to append / to directory names, * to executable regular files, etc.

UPDATE : Based on your comment, l is aliased to ls -CF. Single letter options can be "bundled", so ls -CF is equivalent to ls -C -F. The -C option causes ls to list entries by columns. This is the default if ls thinks it's writing to a terminal; the -C option makes it behave this way unconditionally. (ls -1 lists one entry per line, which is the default if ls is *not writing to a terminal.)

type -a l should show you how it's defined. It's probably set in your $HOME/.bashrc.

(The $ is part of your shell prompt, not part of the command.)