A dry taste (e.g., of sake or wine) — indicating less sweetness and a sharper flavor profile.
このワインは辛口で、魚料理に合う。
This wine is dry and goes well with fish dishes.
辛口の日本酒を一合ください。
Please give me one cup of dry sake.
辛口の白ワインを選んだ。
I chose a dry white wine.
Refers to someone who likes (dry) alcoholic drinks or to a preference for dry drinks — i.e., a person who prefers dry sake/wine or the preference itself.
彼は辛口で、日本酒をよく飲む。
He prefers dry drinks and often drinks sake.
あの店は辛口の品ぞろえが多く、辛口好きには嬉しい。
That shop has many dry options and is pleasing for those who like dry drinks.
A salty taste — indicating a strong salty flavor; in some contexts '辛口' can mean savory or salty rather than dry.
このスナックは辛口で塩分が強めだ。
This snack is spicy/salty with a strong saltiness.
味付けが辛口なので、ご飯がよく進む。
The seasoning is on the salty side, so it goes well with rice.
Harsh or scathing — describing criticism or comments that are sharp and severe.
映画評論家の辛口のレビューが話題になった。
The critic's scathing review of the film became a topic of discussion.
彼女は辛口のコメントで知られている。
She is known for her sharp remarks.
辛口の意見も参考になることがある。
Sometimes harsh opinions can be useful.