The greatest of the medieval flags, the standard was the rallying point for troops in battle. As such, it indicated not the presence of the physical person leading troops, but the office of the leader. Medievally, they were about 8 feet long.
There are definite rules as to what was displayed on a standard. In the hoist (the part next to the pole) was the device of the country or overall allegiance of the owner. The remainder of the flag background displayed the owner's livery colours, upon which were his principal badges and "motto bends" (diagonal stripes bearing the motto). The standard was also frequently fringed along it's entire edge in alternating segments of the livery colours.
Medievally, 'standard' was used as a generic term to indicate any livery flag.