Not in the regular, usual, or established form; not according to official, conventional, prescribed, or customary forms or rules; irregular; hence, without ceremony; as, an informal writting, proceeding, or visit.
On the simplest level, telecommuting makes it harder for people to have the kinds of informal interactions that are crucial to the way knowledge moves through an organization. The role that hallway chat plays in driving new ideas has become a cliche of business writing, but that doesn't make it less true. James Surowiecki
My grandmother was a kind of Scarsdale, New York, society woman, best known in her day as the author of the 1959 book 'Growing Your Own Way: An Informal Guide for Teen-Agers' - this despite being a person whose parenting style made Joan Crawford's wire hangers look like pool noodles. Sloane Crosley
We must ensure that while eliminating child labor in the export industry, we are also eliminating their labour from the informal sector, which is more invisible to public scrutiny - and thus leaves the children more open to abuse and exploitation. Carol Bellamy