A soft fork takes place when there is a change in the software protocol, and previously valid blocks/transactions are made invalid. Old nodes can recognize the new blocks as valid, so a soft fork is backward-compatible.
A wallet that exists as software and stores cryptocurrency on a computer. Most software wallets are more accessible since they are free to generate, however, storing anything on a computer with access to the internet comes with risk.
Solidity is a programming language initially created by Ethereum developers and is the primary language used for Ethereum. Solidity is one of four languages used to target Ethereum's virtual machine which is a principal component of Ethereum based smart contracts.