Mantras in Hinduism are sacrosanct and must not be uttered/chanted injudiciously nor should they be heard or given outside proper procedure. There is rampant disregard for this rule on this forum and people indiscriminately provide all mantras including the gayatri in their answers. I think questions seeking mantras must be deleted as should answers containing them. For this purpose, the definition of mantra should be
Anything that contains a beejakshara
Any portion of scripture that requires a certain procedural chanting and initiation (like the devi bhagavatam/chandi saptasati or sundarakanda)
This rule must be enforced if the purpose of this SE is indeed upholding and propagating Hinduism in its true form.
Kamakoti peetham offers some advice on mantrAdhikAra and dIkSAdhikAra.