The Heist Mode is a cut game mode from Counter-Strike: Global Offensive.
Reference to game mode can be found in
func_bomb_target brush entity from CS GO SDK, where in bush properties description says "This is a Bomb Target designed for the Heist game mode."
On the May 31, 2016 update, was added references Convars to "slow money" it's hints towards to be related with mode:
mp_slowmoney_enabled mp_slowmoney_maxmultiplier mp_slowmoney_minmultiplier mp_slowmoney_multiplierdisplayasbonus mp_slowmoney_rampbias mp_slowmoney_rampend mp_slowmoney_rampstart
In the November 28, 2016 update, Adding to game files new terrorist model named
tm_heavy_riot currently without textures it's possible is related to game mode.
- func_bomb_target on Valve developer Wiki