The LG G5 se has been rumored before, with some saying that it would be a smaller version of the LG G5. After appearing online in Russia, it doesn't appear as though the size rumors played out to be true, but it does have downgraded internals. It won't have the Snapdragon 820 processor, and instead will sport the Snapdragon 652. Another notable difference is that it is said to be a 3G phone, even though the processor has an integrated LTE modem.
Officially announced in Russia, the LG G5 se (H845) is nothing more and nothing less than a slight hardware downgrade of the original meant to bring the handset's price down for more sensitive markets like Russia, Latin America, and possibly other countries. The only differences between it and the regular LG G5 are the processor (lower-spec'd Snapdragon 652 rather than the premium-tier Snapdragon 820), the amount of RAM memory (3GB vs 4GB), and curiously enough - LTE support.
Aside from the internals, the G5 se has the same Quad-HD display, support for the 'Friends' modules, and other features that are included on the regular G5. It is not clear as to where the LG G5 se will be available, we will have to wait for official word from LG on that.