Femboy is a term for gender non-conforming mingender and miaspec people who present femininely in some way. This often refers to clothing and external appearance, but can also sometimes refer to the way one acts, the way one communicates, what interests or hobbies on has, etc. This term has more to do with gender presentation than gender identity, but some femboys may be fingender.
Similar terms include rosboy and femboy gender. Some achillean or vincian femboys may identify as twinks.
Flag
It is unknown who created the flag or when it was created. The light blue comes from the transgender flag. It stands for the masculine-aligned or man-aligned gender, but has only one stripe because it isn't the most important aspect of this identity. Pink represents femininity and gender non-conformity. It is on the outside of the flag because it is one of the first things people will notice about a femboy, and it is the most important and distinct part of this identity. The white stripes represent transgender and non-binary femboys.