Right...without trying to confuse...I am going to use B, C and P to indicate biology, chemistry and physics.
Core science is usually done in yr10 and consists of a bit of B, a bit of C and a bit of P. If you pass B1, C1 and P1 modules you would get a GCSE in 'core science'. Weaker pupils will take 2 years to do this and not do anything described below.
If you do a bit more B and C and P and pass B2, C2 & P2 you get a gcse in 'additional science'
Instead of additional science you could do 'applied science' which would also be B, C and P but the exact topics would be slightly different - less about science 'facts' and more about 'how we use science'.
'double science' isn't actually a GCSE more a description of how many GCSEs you are working to.
So
core science + additional science
Core science + applied science
Core science + astronomy
Core science + phsycology
Could all be described by a school as 'double science' but the cetificate would show 2 different GCSE's.
Triple science pupils will do B1+B2 and B3 to get a GCSE in biology
C1, C2 and C3 to get a GCSE in chemistry
P1, P2 & P3 to get a GCSE in physics.
Note that the B1, B2, C1, C2, P1, P2 are exactly the same as for core and additional science, but if you do the third module for each you get 3 seperate GCSEs instead of core and applied. This would be described as triple but appear on the certificate as biology, chemistry and physics.
Foundation is about the level. For each exam you can take an 'easier' exam called foundation or a harder one called higher. You can't get higher than a grade C if you do foundation. School decides which exam. The level of exam doesn't appear on the certificate - just core science and the grade.