Typographically speaking, it's really a separate kind of dash, a tad bit longer than an en dash. Nowadays it's more often set as an en dash, the em dash is a bi

Typographically speaking, it's really a separate kind of dash, a tad bit longer than an en dash. Nowadays it's more often set as an en dash, the em dash is a bit old fashioned for dialogue. But probably this differs between countries.