Jhānavibhaṅga › Suttantabhājanīya

Abhidhammapiṭaka · Vibhaṅga · Vol. 35 · Section 682

[682] "Neither painful nor pleasant (adukkhamasukha)": that which is mental, neither agreeable nor disagreeable; the neither-painful-nor-pleasant felt experience born of mind-contact; the neither-painful-nor-pleasant feeling (vedanā) born of mind-contact — therefore it is called "neither painful nor pleasant."

English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.