means A word, sound, or phrase repeated to aid concentration in meditation, or more loosely, any saying one returns to again and again as a guiding principle.

from Straight from Sanskrit mantra, a sacred utterance, built from the root man- 'to think' (a distant cousin of our 'mind') plus the suffix -tra, which marks an instrument or tool — so a mantra is literally a 'tool for thinking,' a device the mind uses on itself. It rode into English through the study of Hindu and Buddhist texts and only later relaxed into corporate slogans and self-help refrains.