7 (seven) is the natural number following 6 and preceding 8.. People often abbreviate years using the two last numbers in the sequence, so if it appears that someone might be referring to a time, 07 probably refers to 2007.
Online, the symbol is meant to represent a person saluting, with the o being a person's head and the 7.. As an early prime number in the series of positive integers, the number seven has symbolic.