Supplement to what /u/roastbeeftacohat has already mentioned.

I think the terminology, at least as far as 14th century England is concerned, would be Banneret. According to Dictionary the word is mid to late 13th century french and means little banner (baner+ette). Richardson in his thesis, looking over the accounts of the Tower armouries, uses the term Bannerets when referring to them. Here is context to compare them to the rest of an army, in this case the 1338-9 Flanders campaign.

However, the exact size of the army for the Flanders campaign is recorded in the wardrobe account of William Norwell, which includes full details of the wages for service in Flanders with the king between 22 June 1338 and 16 November 1339. Excluding the garrison of Berwick, Henry Percy’s retinue in Northumberland, and a contingent of south Welshmen employed only during April 1339, the army appears to have comprised 46 bannerets, 235 knights, 1,449 men-at-arms, 79 hobelars and armati, 1,254 mounted archers and 2,478 foot archers (1,284 supplied by the counties of England, 964 from Walers), accompanied by 93 vintenars, 11 standards bearers and 6 centenars. The archery equipment supplied by the Tower was almost enough to equip the whole contigent of 3,732 archers for Edward's expedition to Flanders in 1339.

p.256.

There is also mention of Darcy, John; Latimer, William; Lisle, John de as Bannerets.

p.296, 317, 320

The medieval inventories of the Tower armouries 1320–1410, Roland Thomas Richardson, York, 2012.

In the 100 years war musterrolls, with modern terminology, they are classified as Captain, as opposed to a Commander.