Ive just googled over the web and found a definition that is quite comprehensive for me as a newbie.
So, according to Expressvpn and their glossary, halvening comprises two words "halving" and "happening".
https://www.expressvpn.com/internet-privacy/bitcoin-glossary/
As to the first uses of halving, my investigation brought me back to bitcointalk threads but from outside site, i.e. altcoin wikia http://altcoin.wikia.com/wiki/Coiledcoin that referred to our bitcointalk member thread https://bitcointalk.org/index.php?topic=56675.0
and it dates back to January 05, 2012
So, according to Expressvpn and their glossary, halvening comprises two words "halving" and "happening".
https://www.expressvpn.com/internet-privacy/bitcoin-glossary/
Quote
Every 210,000 blocks, the block reward is halved. Starting from 50 BTC per block in 2009, it currently stands at only 12.5 BTC, after two halvings. Eventually, the block reward will go to zero, after 33 halvings. Also called a halvening (halving & happening), this event is popularly celebrated, similar to a New Years Day of Bitcoin.
As to the first uses of halving, my investigation brought me back to bitcointalk threads but from outside site, i.e. altcoin wikia http://altcoin.wikia.com/wiki/Coiledcoin that referred to our bitcointalk member thread https://bitcointalk.org/index.php?topic=56675.0
and it dates back to January 05, 2012