A Tribute Summon (called Advance Summon (アドバンス召喚, Adobansu Shōkan) in the OCG, previously called Sacrifice Summon) is a form of Normal Summoning a Level 5 or higher monster by Tributing another monster(s) you control. Level 5 and 6 require one Tribute, while Level 7 and higher require two Tributes.
Some cards can avoid the Tribute Summoning rules. For example, "Fog King" can be Tribute Summoned with one Tribute, or "Normal Summoned" without a Tribute. "Mausoleum of the Emperor" allows you to pay Life Points instead of Tributing monsters, but the Normal Summon then cannot be considered a Tribute Summon.