Alankar literally means ornament or adornment, and it carries two related senses. In the first, it is the family of melodic decorations — meend, gamak, murki, khatka, andolan — that turn a bare succession of swaras into expressive music.
In the second sense, alankars (also called paltas) are the systematic melodic exercises every student drills: fixed patterns run up and down the scale (Sa-Re-Ga, Re-Ga-Ma…) to build control and to learn how a raag moves. These paltas are the scales-and-arpeggios of Hindustani training.
Both senses share the idea that melody is "adorned" — whether spontaneously in performance or methodically in practice.