counter
counter for packages, luggage, etc.
Used to count individual items of luggage, parcels, or similar discrete objects, especially in shipping or delivery contexts.
宅急便で荷物を三個口送った。
I sent three packages by courier.
counter
counter for electrical outlets (of a power strip)
Specifically used for counting the number of outlets on a power strip or similar multi-socket device.
六個口の電源タップを買った。
I bought a power strip with six outlets.
Compound of 個 (counter for individual items) and 口 (mouth, opening), literally 'individual opening'. The exact historical derivation is uncertain; the spelling is conventionally associated with counting discrete units or outlets.