A samurai without a lord was called a Ronin
Ronin are samurai without a master
The difference between a shogun and a samurai is like the difference between a king and a knight.
When a Samurai has no master, they are referred to as Ronin I believe.
Ronin who were master-less Samurai .
they are the positions in which a samurai serves his daimyo
The samurai were responsible only to their master who in turn were part of a chain of alliances ranging up to the emperor. Samurai had no lateral responsibility and if told to attacker kill an equal would do so without hesitation. Ronin (masterless samurai) were pretty much on their own. Challenges were e met, failure to accept challenges was not an option for samurai or ronin.
A masterless Samurai is called a 'Ronin' (literally: drifting person).
You may may be thinking of 'Ronin', who were Samurai without a master to serve.
Rurouni Kenshin or Samurai Champloo
Emperor, Shogun, Daimyo, Samurai*, Peasants, Artisan, and Merchants. *There are also Ronin, which are Samurai without a Daimyo (because he/she was killed, committed seppuku, etc.).
浪人 (Rounin) - a lordless samurai. It's made up of two kanji characters.