In fashion; fashionable (1,2,4)
I believe the answer is:
a la mode
I believe this is a double definition.
'in fashion' is the first definition.
(I've seen this before)
'fashionable' is the second definition.
(a la mode can mean trendy or fashionable)
(Other definitions for a la mode that I've seen before include "Fashionable (French)" , "Up to date" , "In the fashion - in France" , "In fashion - served with ice cream" , "Do a meal in French style (1, 2, 4)" .)