Arguably the most popular match up due to flexibility and variance in the match ups, in this match up both players have to play and respond quickly to threats as the game can tilt almost immediately. Terran nowadays usually go for a fast expansion play on then, Zerg usually responds to this by either double expanding or go for a real fast mutalisk harass, mutalisk these days are just so powerful due to the mutalisk stacking trick (group any number of mutalisk + 1 overlord and the mutalisk will clump up together automatically), an early expansion by either players means that early aggression by the side that expand quickly is severely limited, putting himself in a defensive position for better economy.

During this mutalisk harassment period, the zerg has map control and usually will expand once and tech to lurkers, this is due to fact that mutalisk get less effective when the terran player gets more and more marines. If the zerg chooses to double expand after he sees the terran player early expand, the zerg and choose to go for later muta harass (about a minute late) or tech straight to lurkers (riskier). The terran in both situations (muta harass, double expand) can exert some limited form of aggression like sending a group of marines + medics to attack the zerg, forcing the mutalisk or the lurkers to return to defend (which usually will end up killing that small party). During this camping period in his base, the terran usually techs to science vessels(crucial for detection to prevent stop lurkers)

Once the terran gets his first vessel (about 9:30, also called the 9 min push) he usually launches a push which is very very hard to stop for the zerg, during this period when the zerg loses map control, he is already teching to hive to get defilers and normally when the terran reaches the door step the research for consume is usually completed, allowing the defiler to cast dark swarm(range attacks without splash deal zero damage to units under dark swarm) to protect his base. The game the plays on when the terran tries to get his 3rd base(which will allow terran to get a larger army and more vessels or tanks) while the zerg tries to get his 4th gas base(which will allow the zerg to transition to Ultras).

This is arguably my best match up (though not very good) and arguably the best match up of most terran players. This is also a matchup where sick sick micro can occur that will change the side that is winning. After reading this article, you would wonder why do zerg players favour lurkers over hydras, the reason is simple, hydra do explosive damage per shot and explosive damage only deals 50% of the original damage on small units which results in medics healing faster than the hydra can kill a marine. Lurkers however deals melee damage (that is why it deals damage under dark swarm) so marines melt when they get flanked by lurkers and zerglings(which is used to soak damage).