Jitterbug & Jive

Essentially, Jive & Jitterbug are the same dance as LindyHop using many if not all the same moves - albeit with an emphasis on simpler 6 beat footwork which can suit faster tempo music better. Jitterbug is generally a fast moving and visually impressive dance style and is usually associated with 1940's re-enactment societies.
Essentially, Jive was born through American Army GIs interprtation of Lindy Hop (a dance that has its roots in African-American society). A Jitterbug may also refer to a Swing Dancer.
The differences between Jitterbug, Jive & Lindy Hop are minor - generally, it seems that Jivers & Jitterbugs are more concerned with 1940's recreation than Lindy Hoppers - though this is probably contentious.

This is what wikipedia says about Jitterbug

Modern Jive

Invented in the 1980's by James Cronin of CEROC fame and franchised across the UK, Modern Jive although popular in the UK remains practically unheard of elsewhere. Its popularity has led to many independant organisations teaching the style that has become more commonly known (through some revisionistic re-writing of recent history) as Modern Jive.
Similarly, CEROC nee Modern Jive is said to be based on French Jive, but the only references to French Jive is in UK texts. The French dance Rock'n'Roll or Swing dance styles such as Lindy Hop, Balboa and Shag. Modern Jive was infact most closely related to 1970's partnered Disco dancing (the Hustle) as in John Travolta's 'Saturday Night Fever'

As a basic dance style, Modern Jive readily integrates movements from other unrelated dance styles. Modern Jive (in its various franchised forms) seems gernerally to be gravitating increasingly towards Latin Ballroom styles and Salsa (which is a similarly 'army' dance style) sharing many upper body movements but with the addition of more structured footwork.

Modern Jive, typified by organisations such as CEROC and LeRoc is not a Swing Dance style (though it can be danced to mid tempo Swing & Jazz music) since it uses a two-step (step in, step back ...) walking style.

Little emphasis is placed on learning footwork patterns which is its strength (since it is therefore easy to learn) but also its weakness (since the style is ultimately limited to mid-tempo music).

This is what wikipedia says about Modern Jive

This is what wikipedia says about CEROC