@Tij it's a place in memory
processors are basically very very fast calculators, they manipulate numbers in fancy ways to do cool things
one small problem, processors themselves can't remember a lot of numbers, you couldn't actually store an image or executable inside the processor's "memory"
so we have random access memory (ram), it's just a place that the cpu can write and read numbers from, a huge amount of numbers
and the way you know where to read and write to a place in memory is with a memory address, which is just a number telling a position in memory

memory is linear, let's say your ram starts at all 0
so your memory would look like
0 0 0 0 0 0 0 0.... billions of time
if the processor ran a command to write value 45 to address location 0x4 (0xnumber is just the notation for writing a number in base 16, hex numbers are usually used for address instead of decimal because of some nice properties)
your memory would become
0 0 0 0 45 0 0 0...
(note that 0x4 is the same as decimal 4 but it was written to the 5th location in memory, that's because memory starts at 0)
then the processor can later read that number to do math with

there's more to it but that's the basics, just a number to a location of one (ore more) numbers in ram