The main difference between a satchel and a briefcase is that a satchel is soft-sided. Also, satchels often have straps while briefcases usually don’t.
In literature, the satchel is often associated with the classic image of the English schoolboy: “And then the whining school-boy, with his satchel” is a phrase from Shakespeare’s monologue “All the world’s a stage”.
Today, satchels are very popular and fashionable. The newest trend has been the the introduction of satchels in fluorescent and metallic colours, mostly worn by women.