Soldity can't handle floating point numbers so it must store decimals in integer form.
1e<n> notation basically means "1 followed by n number of zeros". So 1e2 is equal to 100 and 1e4 is equal to 10000, and so on.
444 * 1e6 * 1e18 then means:
1000000 (6 zeros)
1000000000000000000 (18 zeros)
TOKEN_LIMIT = 444 × 1000000 × 1000000000000000000
444,000,000 total tokens (444 × 1e6), but taking account decimal places (the SOMN token supports up to 18 decimal places) it then becomes (444,000,000 × 1e18).
TLDR; 1eN is exponential notation, to better represent the number of zeros. Solidity only supports fixed-point numbers.