Whilst Midgardsormr is right about the "Solo" being the boss, it stands apart from the "roles" mobs are given, as you can get a "Solo Brute".
In 4e you get 4 monster types:
Minions - Like a standard mob, but killed with 1 hit
Standard - Normal mob, normal powers
Elite - A tougher than normal monster/enemy that is usually the strongest in a group (so the Orc Leader who leads the tribe of orcs)
Solo - Typically a standalone mob that is meant to, as the name suggests, fight solo (eg. a Dragon, Sith Lord, or any encounter where combat can still be fun with only 1 target)
In the 4e DM guidebook that Midgardsormr mentions they do actually refer to Elites and Solo's as "Elite and solo monsters represent the toughest foes the characters can face... They make great villains, stars of a campaign, or intimidating "boss" monsters at the climax of an adventure".
Basically, anyone who is going to be overly picky about the term they use should just be ignored; some people will find fault in anything
This is a area that computer gaming, table top gaming, mmo, actually almost all gaming has a similar thread. The bosses, the Big boss, Epic Boss, The big guty, etc. are different terms for the same object. The goal of many adventures is to get or defeat the boss. So using ideas from other platforms (table top, computer, arcade, etc.) works well. Even using ideas from different genres. Remember the Greeks stated that there are only 6 or 7 original plot lines. It is how you tell the story that will matter.
Anything used to describe a tool or mechanic that crosses the platform of said games is fair game. That said whatever you choose to use will have impact on the mindset and atmosphere of the encounter. Using "boss mob" to me indicates something not to be engaged with, more just game furniture to further you on the way to blinging out your character.
Personally we always used the "villain" or "bad guy" to our main opponent. "Fodder" would be for goblins and the rest of the guys that we fought through. Except our DM had a penchant for trying to balance our encounters "perfectly," ie. so that'd we have a 50/50 chance of winning or loosing, and then he'd fudge his way out so we'd maybe survive. So "fodder" never really applied, it was more like crack squads of ambushing ninja bears and very threatening well executed divisions of goblin stormtroopers. We were the fodder really...