A tam o’ shanter (in the British military often abbreviated to TOS) is a name given to the traditional Scottish bonnet worn by men. The name derives from Tam o’ Shanter, the eponymous hero of the 1790 Robert Burns poem.
This definition is taken from Wikipedia but there is also a definition for a tam worn by women.
The tam was a millinery design for women based on the tam o’ shanter military cap and the beret. Sometimes it was also known as a tam cap or the traditional term tam o’shanter might also be used. It became popular in the early 1920s, when it followed the prevailing trends for closer-fitting hats that suited shorter hairstyles and for borrowing from men’s fashion; other traditional men’s hats that rose to popularity in women’s fashion during this period included the top hat and bowler.
You can read more on this on Wikipedia. I think I can be safe in saying it is a tam.
The pattern was taken from this booklet and I used wool which had been frogged from a previous project that no longer fitted.