U - which is thermal transmittance also known as U-value defines the rate of transfer of heat
through one square metre of a structure divided by the difference in temperature across the structure.

Uw - value concerns whole window including frame, glass and swiss spacer.  

Ug - is factor for glass unit.

Thermal conductivity is the ability of the material to conduct heat,
the smaller the value of thermal conductivity the better insulating material it is.

Light Transmittance (TL) is the proportion of visible light at near normal incidence that is transmitted through the glass.

Total transmittance (also known as G value or solar factor) – the proportion of solar radiation transmitted through the glass
 by all means. This is composed of the direct transmittance and that which is absorbed by the glass and reradiated inwards.

SBD(secured by design) is a project introduced by police in 1989 in order to make doors and windows more secure against burglary.
Further evaluation of the problem resulted in developing PAS 24 regulation.
Doors and windows need to be tested in order to get PAS 24 certified.