noun
one's regular inn; one's usual hotel
Refers to a lodging place (inn, hotel, ryokan) that one habitually stays at, often while traveling for business or on regular trips.
出張のときはいつもあの定宿に泊まる。
When on business trips, I always stay at that regular inn.
京都に行くときは、もう決まった定宿がある。
When I go to Kyoto, I already have a regular place to stay.
行きつけ refers to a place one frequents (restaurant, bar, shop), not limited to lodging. 定宿 is specifically for accommodations.
Compound of 定 (じょう, 'fixed, regular') + 宿 (やど, 'inn, lodging').