Raft algorithm: What's the data format of `term`?

Question

Time is divided into terms, and each term begins with an election. After a successful election, a single leader manages the cluster until the end of the term. Some elections fail, in which case the term ends without choosing a leader. The transitions between terms may be observed at different times on different servers.

In Raft algorithm, term is a limited period of time, and widely used in leader election, log replication.

1. What's the data format of term?

2. Is it composed of Unix timestamp and length ?

3. How does every node guarantee their timestamp are synchronous? (Google Spanner use Atomic clock to guarantee true time).