Co.

1 the abbreviation of company: James Smith & Co.

2 and co spoken used after mentioning a person or thing to mean the other people or things that you consider to belong to their group: I can't say I'm looking forward to seeing Angela and co again.

3 the written abbreviation of county: Co. Durham

c/o the written abbreviation of care of; used especially in addresses when you are sending a letter or parcel to someone who is living in someone else's house etc: John Hammond, c/o Dowling Music College, Bethesda, Maryland