There are broadly two categories of electronic signature, ‘basic’ and ‘advanced’. Advanced esignature refers to technology-based signature, typically using encryption methods. In advanced esignature the technology itself holds the evidence of the signature.
The most commonly used advanced esignature is Public Key Infrastructure (PKI). While not originally designed for executing documents, the elements of PKI make it a good match for demonstrating a signature.
By comparison ‘basic’ esignature is a process-based signing method, where the evidence of actions (performed and recorded on an electronic device) of an individual in association with a document that holds terms of an agreement generates the signature.
These explanations beg the question, ‘what is a signature’ or ‘what are the elements that create a signature’, in a legal context. It’s a common assumption that the only way to form a contract is to write a handwritten name. You can agree a legal contract verbally, or even by behaving as if you have.
A signature, both electronic and ‘real’, is more fundamentally an expression of the coming together of individuals over the terms of an agreement between them, a consensus between those parties over those terms and how those terms are agreed, with the intent to create a legally binding obligation.
This is a general guide and not legal advice. Signatures and the requirement for signature will also vary by the nature of the contract and jurisdiction that governs it.