This term and commonly used phrase stands for 'little girl' and is pronounced 'el-gee'. The girl referred to maybe not necessarily a slut, but a girl around the age of sixteen or below who is renowned for attempting to appear older than their actual age. For example many try to simulate wild nights they have seen their siblings participate in while others affiliate themselves with sixth formers and university students, sometimes successfully having relations of an intimate nature with them. Many go on to boast about these events, often lying about details. The term was coined in Bedford School by the renowned LG Bandits, also known for coining other key phrases of the time. Another related phrase is 'TLG' (tasty/too little girl) referring to a girl who is too young or young but very very good looking.
"Mate, your such an LG hunter/bandit"
"That LG got dealt wiv"
"Man, how waste are LG's these days"
"I cant wait till that LG is legal"
"LGs lookin too buff these dayz"