What does it mean? What should you do?
Your e-cigarette generates vapour by heating your liquid. The design is much like a kettle: you have a heating element - your coil - which gets hot enough to vaporize your liquid. The way in which the coil produces heat is through its resistance or 'ohmage'.
When you run an electrical current through a material you are moving electrons (small negatively charged particles) through it, usually from the positively charged side of it to the negatively charged side of it. The ease with which these electrons can move in a material can be called its 'resistance'. The level of resistance a material has is referred to as 'ohmage'.
So how does this generate heat? Well, any time electrons move you will generate a certain amount of heat... the more difficult it is for them to move, the easier it is to generate that heat. Think about being at a gig or in a crowded room. Takes a lot of effort to get to one side from the other and you have to push your way passed lots of other sweaty people; especially if they're all trying to get to the same door when it's over! If you're in a wide open field then this is a lot easier! But, in that open field you will have enough room to run and if you do this you might be just as hot and sweaty as if you were trying to get out of the concert... probably even more so!
Sub-ohm vaping means that the resistance of your heating element (coil) is less than 1Ω (that little symbol is an 'omega' and used to represent resistance) which means it's quite easy for the electrons to flow. Therefore, to heat it up you need to expend a lot more energy - running in a field vs walking at a gig - which is why you will require a lot more wattage (also called 'power') to get your heat and produce vapour. Because the resistance is lower, you have more opportunity to generate heat and so generally speaking sub-ohm coils will be able to produce much more vapour than those with a resistance of greater than 1Ω.
It's not all just 'mega-clouds' though... you need to be careful! Because you are using more power, your batteries are being placed under more strain. Always make sure any battery - or mod - you use is rated to go up to the wattage your coil is requiring it to use. Usually your battery - or mod - won't allow you to set it above where it's rated but this still might not be enough. If your battery - or mod - allows you to change the rechargeable batteries within it you need to make sure these are good quality. If they aren't and/or you try to draw too much power through them then they're going to get too hot and possibly vent (see: 'go bang'). If your mod uses 18650s (18mm diameter, 65.0mm height) then we recommend Samsung 25Rs. However, we recommend you do you own research into battery safety and suggest an online reviewer called 'Mooch'.
Because you're producing a lot more vapour with sub-ohm vaping, you also want to make sure you're using the correct liquid: to find out which check out our blog post!