The Chakra Transfer Technique allows the user to transfer some of their chakra to another person.
This technique was originally created by Hagoromo Ōtsutsuki in order to "connect" the spiritual energies of every living person. His intention was for it to be used to build and maintain peace through his religion of ninshū, but this technique ended up becoming another tool for war when humanity weaponised chakra. This technique is used by many shinobi, each one of them has shown to use technique in different ways.
Certain people, such as Minato Namikaze and Naruto Uzumaki could also mould the transferred chakra in order to adapt it to another person's specific chakra type. In the latter's case, due to Kurama's chakra, it also enveloped the recipients in a chakra cloak similar to his "Version 1" form, albeit with no tails. Once, the user transfers its chakra, he/she is able to manipulate that chakra remotely.
Katsuyu and itssummoners have a unique bond between them through Strength of a Hundred Seal and they can use Katsuyu: Immense Network Healing. Tsunade used this technique during Pain's invasion of Konoha, with Tsunade first transferring her healing chakra to Katsuyu, and then Katsuyu itself transferring it to the wounded villagers. Sakura used the same method of Tsunade with Katsuyu to heal wounded shinobi in Shinobi Alliance against Ten-Tails.
Tailed beasts are also able to freely share their chakra with whoever they choose, and as Kurama has noted, it is a less complicated process for them than it is for humans.
Hagoromo Ōtsutsuki is the first user of this technique to connect all humans living in the earth and gave the chakra to humanity besides their family. Hagoromo also used this technique inside of Naruto and Sasuke who are the reincarnations of Asura and Indra. He gave the power to them to defeat Madara. While using this technique, a unique entity appears behind Hagoromo which is similar to himself possess two empty eyes and a marking reminiscent of a third eye in its forehead.
If the Aburame member has proper control, the kikaichū are also shown able to transfer their accumulated chakra to others targets, replenishing them.
The Magaki Group uses this technique in a different way. First Nangō sends his chakra to Benten and Chūshin, and then both of them send it along with its own to Akaboshi, greatly enhancing the power of his techniques. He is able to shatter a barrier easily with his increased chakra.