A little is someone that likes to act younger then they really are. It's kind of like having an alter ego that's much younger then yourself. Most littles don't act little 24/7, but when they do slip into their younger alter ego it's called slipping into headspace.
When a little is in headspace that is when they are at their most submissive and most vulnerable, and sometimes even talk higher pitch or with more of a lisp then normal. They're more prone to emotional outbursts like throwing a tantrum or getting overly excited about something. They are also the most needy in this state, as they are not thinking like a grown up but like a child, and need a bit more guidence and reasurence. Some littles are shyer in headspace while others may become more outgoing. Every little is different and has their own headspace unique to them.
The age range for littles is very broad and can range from newborn baby to toddler young child. 0-8 is usually the agreed range. It could be a fixed age like 3, but it could also be a range like 2-6.
Littles tend to enjoy more childlike, babyish items such as pacifiers, sippy cups/bottles, stuffed animals, picture books, toy, games, younger looking clothing, pull-ups/ diapers, ect. Clothing and little items are different for each individual little.
Terms for relationships:
DDLG = Daddy Dom/Little Girl
MDLB = for Mommy Dom/Little Boy
DDLB = Daddy Dom/Little Boy
MDLG = Mommy Dom/Little Girl
CGL = for CareGiver/Little
Little: Could I have another cookie please?
Caregiver: Yes sweetie, but only because you asked so politely.
Little: Thank you! I'm gonna finish coloring my dino picture for you now!
Caregiver: You're welcome honey. I can't wait to see your dino when it's finished, I'm sure it looks amazing already, baby doll.