What does c/o stand for in a postal address? [closed]

Solution 1:

c/o here stands for care of. The letter is to be delivered and entrusted to the care of John Doe, who will be responsible for seeing that it gets to Joe Black.

care of on Wiktionary

Wiktionary also suggests c/- is common in Australia and New Zealand.

Solution 2:

In the UK, "Co." would normally stand for "Company", at the end of a company name.

Despite the non-capitalisation of "co." in the title, my first thought was "Joe Black Company". This is often used (or used to be) in a format such as "Joe Black Co. Ltd." meaning "Joe Black Company Limited".

The most common abbreviation in the UK for "care of" is "c/o", so we would have written

Joe Black c/o John Doe

In fact, I note that the Wiktionary link given by @NateEldredge gives "c/o" as the first abbreviation listed, and does not even list "co".