Hello there and welcome to SalonGeek!
I'm not surprised you are confused, there is a lot of information out there and much of it is contradictory. It takes a little experience to be able to navigate confidently through the large and diverse professional nail industry we have today.
Bear in mind that different companies give different names to their products, not because there is some standard naming code they have to adhere to, but because it suits them and their product range at the time. Some companies choose to use the most commonly used terms to name their products and some choose to use new and different sounding names to help set themselves apart - which is all very well and good, but they don't go into a pan-brand glossary unfortunately. So navigating all this when you are new to the industry is much easier with a tour guide! That's where SalonGeek can come in very handy. It's also a good idea to find some impartial Facebook groups, such as this one:
https://www.facebook.com/groups/NailProfessionalsTechnical/
To answer your question, here is a little Gel terms glossary:
Permanent Gel, Buff-Off Gel
- A gel that does not remove (soak-off) in solvents like acetone and needs to be filed off. Usually available in clear, pink opaque pink and white but can be mixed with glitter or pigments to customise the colour.
Removable Gel, Soak Off Gel (SOG)
- A gel that can be removed in acetone. Usually requires a little filing first before soaking, but not always. Usually available in clear, pink opaque pink and white but can be mixed with glitter or pigments to customise the colour. Some companies manufacture soak off gels that are already pigmented and sell them as a range of 'coloured gels').
Hard Gel, Sculpting Gel
- A gel that can be sculpted to create structure, i.e, an apex. Can be used with Sculpting Forms, Tips or simply straight on to the natural nail. Can come in a permanent or a removable form. Usually available in clear, pink opaque pink and white but can be mixed with glitter or pigments to customise the colour.
'Builder Gel' could go into this category.
Soft Gel
- In my opinion a pretty out of date term that doesn't really tell us anything. Could mean a soak off as opposed to a buff off gel, but could also mean overlay gel, both of which come in removable or permanent forms.
Overlay Gel
- Intended to be applied in an even layer over the natural nail. That is, not for extending length and not for building structure/an apex. Usually available in clear and could be mixed with glitter or pigments to customise the colour. Some companies manufacture overlay gels that are already pigmented and sell them as a range of 'coloured gels').
Can anyone else add to this? Give us a second opinion?