Pajamas and pyjamas both mean loose-fitting clothes worn for sleep. Pajamas is the preferred spelling in American English. Pyjamas is preferred in most varieties of English from outside North America. Canadians are inconsistent on the issue, though they prefer pyjamas by a small margin.
Examples
For example, these non-U.S. publications use pyjamas:
Munshaw-Luhar says the shops also stock sherwani suits and kurta pyjamas for men and expensive wedding outfits. [Sydney Morning Herald]
What I always do is to retire to the bedroom and change into my pyjamas. [Financial Times]
Padding around the house in pyjamas and bunny slippers won’t do your sexual relationship any favours either. [Ottawa Citizen]
And these American publications use pajamas:
He’s wearing red silk pajamas, a black smoking jacket, black slippers, white socks. [Vanity Fair]
The nightwear comes in a handful of styles and colors and includes nightgowns and pajamas. [Chicago Tribune]
Many wore pajamas, masks or wigs. [Wall Street Journal]
