The term hamon (kanji: 刃文) means "blade pattern" in English. It is written はもん in hiragana. It's pronounced roughly like "ha-moan".
Also pronounced jinmon. 刃 means blade and may also sometimes be pronounced yaiba. Yaiba derives from yakiba (焼き刃, “quenched blade”) and is apparently the product of a phonetic change.
文, pronounced mon, means pattern in this case. It can also mean sentence (in the grammatical sense), as in the word kyomon (経文, sutra). It is also pronounced bun and means sentence or any writing, as in the word bungaku (文学, literature).