Ronin

A ronin was a samurai with no lord or master during the feudal period of Japan. A samurai became masterless with the ruin or disfavor of his master.

Status
In the bushidō Shoshinshu (the code of the samurai), a samurai was supposed to commit seppuku (also "hara kiri", ritual suicide) with the loss of his master. The samurai who didn't commit seppuku were dishonored and shamed in japanese society.The were on their own, and were unwanted by other samurai and daimyo (the feudal lords).

Like regular samurai  wore their two swords. Many often those low on money, would carry a bō (staff around 5 to 6 ft) or jō (smaller staff or walking stick around 3 to 5 ft) or they would use a (bow). Many weapons reflectedd off what ryu or bujutsu school they came from when they were samurai.

Nara and Heian Periods
The word rōnin literally means "wave man". The term originated in the Nara period, when it referred to a serf who had fled or deserted his master's land. In the Heian period, the word refered to a samurai who, in any way, left his master. This included the master's death in the event the samurai doesn't commit seppuku.

Kamakura and Muromachi Periods
In the Kamakura and Muromachi periods,when samurai held lands, a was a samurai who lost his lands. With frequent battles several daimyo needed to augment their armies, recruiting many restoring the status as samurai. Those who didn't find new masters often joind bands, becoming thieves and murderers.