Why DTMF stands for Dual-Tone Multi-Frequency: each keypad digit sends two audible tones at once, one from a row group and one from a column group, and the repeater's decoder identifies the digit from that unique pair. It is the same touch-tone signaling used by telephones, and hams use it for autopatch, remote control of repeater functions, and linking commands.
Watch out CTCSS is the tempting one, but it sends a single sub-audible tone below 300 Hz that simply unlocks the repeater's receiver, not a pair of audible tones. D-STAR is a digital voice and data mode, and GMRS is a separate licensed radio service entirely.
DTMF = Dual Tone, two tones at once. CTCSS = one quiet Continuous tone.