Hi,
One definition is ..
'Moving from one stage to another'
Collins handbook pg 7 or
free dictionary
A transition might happen smoothly, cause anxieity or uncertainty.
http://www.silkysteps.com/forum/showthread.php?t=13254
Ideas on supporting trasitions:
http://www.silkysteps.com/forum/showthread.php?t=13264
Hth xx