Thanks to all!
The witness Segregrated or often abbreviated as SegWit is one (Hard Fork) proposed for Bitcoin software, which is designed to correct a variety of serious problems. SegWit is an update to the Bitcoin system. The core that replaces the problem. This is done by dividing the transaction into two segments, adding the initial signature of the added part and adding it as a separate structure in the end. The original section will continue to save the sending and receiving data, while the new "Witness (Signature)" structure will contain digital scripts and signatures that are useful as transaction validation. The original data segment will be calculated normally, while the "Witness" segment will be calculated only by 0.25% of the actual size.
SegWit itself adds to provide additional speed by reducing the Signature size for each transaction to only a quarter. By reducing the burden on each transaction, it is expected that the Bitcoin transaction process will become lighter and faster, spending Bitcoin currently increasing scalability (scaling) is more serious and getting worse over time.
SegWit is also trying to overcome the flexibility of transactions that have become Bitcoin's weak point to date. Although this bug vector is not harmful to direct users, it is difficult to solve this problem, so Hard Fork SegWit must be done to patch the gap