What does Tg<0 deg C and no maximum operating temp mean?

Curious as to what this tg means, can anybody translate?

How flexible is this ?

http://www.resoltech.com/IMG/pdf/DS-1600-V5.pdf

The data sheet lists a Tg <0C which simply means this resin is in a “rubbery” state above 0C and a “glass-like” state below 0C. This resin is very flexible and almost rubber like. It appears to be extremely flexible, the elongation at break is 55% whereas a typical epoxy is closer to 5%. “Max operating temp yet to be defined” = we don’t know the max operating temp

Thanks for that!