Geth, short for Go Ethereum, is a command-line interface that allows developers to run full Ethereum nodes, mine the cryptocurrency and execute smart contracts.
Geth is the command-line interface for one of the three main code components of the Ethereum blockchain. Go, a programming language developed by Google, is one of the languages used to build the Ethereum network, and Go Ethereum is the interface used to write, edit and manipulate the Go code for the blockchain. Aside from Go, the Ethereum blockchain and protocol are also heavily based on Python and C++
Geth is the easiest and most accessible way for a developer or investor to run a full Ethereum node. Because of the user-friendly interface, Geth allows developers to quickly create accounts and start editing and improving the Ethereum network code. As a completely open-source project, Geth allows developers to get to the very foundation of the Ethereum blockchain and work on bugs and possible improvements. All source codes for Ethereum are available in Github and developers have free access to them, as well as read and write permissions. Currently, there are more than 400 people who have contributed to the Ethereum blockchain code. Of course, some of them are more involved than others, so people like Jeffrey Wilcke and Péter Szilágyi who have written major portions of the code are considered top contributors.
Go Ethereum is a very important part of the successful operation of the Ethereum network. Because it provides the easiest way to run a full Ethereum node, a lot of node-operators rely on Geth to be able to perform their tasks as validators. Without the Geth interface, the Ethereum network might not have been as successful as it is at the moment. Running full nodes is an essential requirement for the blockchain to be successful and active. Node operators are the ones who validate transactions and make sending and receiving ETH possible. Without software like Geth operating a full Ethereum node might not have been as easy, or accessible.
Last but not least, as the official Etheruem network client, Geth is the safest way to be an active participant in the network. While there are public node providers, the security of your node is at risk with them. If you instead decide to run your own, private Ethereum node through Geth, both your information and the network as a whole are going to be better protected. With a private node, you will essentially have a copy of the whole Ethereum blockchain, against which you will verify transactions. This increases the level of security, as the more private nodes there are, the lesser the chance for successful malicious attempts. Cryptocurrencies and blockchains are innately secure because of the peer-to-peer type of system, where node operators participate in securing the network together.