What are SegWit, BIP148, UASFs and UAHF?

There are still many bitcoin users don't understand the term of SegWit and other new isuues like UASF and UAHF. This explanation may help you to understand them.



SegWit stands for Segregted witness. It is a software to improve max block size proposed by bitcoin core developers. Segwit is the key or multiple Bitcoin  Improvement Proposals. (BIP) either 148 0r 149. 

A user-activated softfork (UASF) is a general method of deploying softforks (like SegWit). UASFs have been done in the past, both by Satoshi and after Satoshi left. Unlike the BIP9 deployment method originally planned for SegWit, a UASF does not require any miner cooperation. A UASF can fail, but only through insufficient economic adoption, not by any miner action. However, splits are more likely with UASFs than with BIP9 deployments, especially when the UASF is done on a compressed schedule. (For ideally-low split risk, a UASF would take about a year to activate.)

BIP148 is one specific UASF. It is intended to activate SegWit. It activates and may cause a split on August 1. If it succeeds economically, it will activate SegWit by November.

The large Bitcoin miner Bitmain announced that they might engage in a (nonsensically-named) "user activated hardfork" ("UAHF") shortly after BIP148 activates if BIP148 has any success. This would definitely cause an additional split, resulting in up to three currencies: BIP148-Bitcoin, Bitmain-coin, and (depending on the degree of BIP148's success) status-quo-Bitcoin. As mentioned previously, if you have x BTC before the split, you'll be technically able to claim x of all three of these currencies after the split. Source https://bitcointalk.org/index.php?topic=2012799.0

SegWit has been applied in Litecoin and made succesful.
http://www.coindesk.com/litecoin-successfully-activates-long-debated-segwit-upgrade

In bitcoin activating SegWit has become long debate among developers, miners and bitcoin users. Some of the users panic waiting for 1 Aug. 1 Aug will be the fnal date of the application all the bitcoin improvement program. All program has benefit but there are some negative impact to the bitcoin community and the blockchain itself. The worst possibiitiy is split chain. Now people are waiting for the Aug 1. I think you'd better read Are you prepared for August 1?.