"Moon Crystal Power" is the phrase that Sailor Moon says to heal the Spectre Sisters as human women using the great powers of the Silver Crystal. She also uses this phrase during her final battle with Wiseman, to try and heal Black Lady and to awaken Neo-Queen Serenity. In the DiC English dub, it is renamed Moon Crystal Power Activation/Power when she healed the Spectre Sisters. Other times it retained the name.
Later in the anime, Sailor Moon would use the command "Moon Crystal Power" to call upon the power of the Silver Crystal without directing it into a specific attack, similar to how the Sailor Senshi would call upon the power of their guardian planet. As one example, at the end of the Sailor Moon R movie when the Inner Senshi combined their powers with Sailor Moon to redirect the asteroid, Sailor Moon used this command to call upon the Crystal's power.
Chibiusa also used this command in Act 49 of the manga, when she and the other Senshi combined their powers to aid Sailor Moon's Starlight Honeymoon Therapy Kiss attack. She also transformed into Eternal Sailor Chibi Moon.