Viral damage is Virus. It amplifies damage to the health of the afflicted target by 100% for 6 seconds. Subsequent procs add 25% increased damage to health up.
Heat damage is Ignite. It sets the enemy ablaze, which makes them panic, reduces their armor by up to 50% and, after a 1 second delay, deals a tick of damage every second for 6 seconds.
Slash Damage is one of the three physical damage types. It is effective against all forms of flesh.
Primary Merciless is a Primary Arcane that on kill increases primary weapon damage for 4 seconds and stacks up to 12 times. At max rank, it also passively increases reload speed.
source: https://warframe.fandom.com/wiki