Full Faction refers to a deck, of which all of the runes are of the same faction. This type of deck, and Split Decks, are the only deck structures currently allowed in Ranked Play, and are considered to be "regulation" decks. The Training Grounds, Daily Missions, and Campaigns all allow the use of "non-regulation" decks.
A Full Faction deck will recieve a faction bonus, according to the faction used in the Full Faction deck.
Full Faction BonusesAugment
SL - Champions you control take 20% less damage (after DEF), with a minimum reduction of 1, from attacks.
FS - You recover 6 nora at the start of each turn.
FW - Champion runes you own have their cooldowns reduced by 60%
IS - Champions you control take 6 less damage from spells.
KF - Champions you control have +1 SPD and +1 maximum AP.
ST - Champions you control have +10 maximum HP.
SP - Whenever you deploy a Champion, you gain 8% of its Nora cost. When that Champion is destroyed, you gain 4% of its Nora cost.
UD - Champions you control with a maximum range of 3 or less receive a +4 DMG buff. Champions you control with a maximum range above 3 receive a +2 DMG buff.