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Definition
TTL, or Time to Live, is a value that determines how long data should be kept before being discarded or refreshed. In networking, it is often used in DNS settings and packet headers to limit how long a data packet or record remains active on the internet or within a network.

Why it matters
TTL helps control data flow and system performance. In DNS, a shorter TTL means updates to records propagate faster, while a longer TTL reduces the number of DNS lookups. In routing, TTL prevents data packets from circulating endlessly by setting a maximum number of hops.

Example use case
A website’s DNS record has a TTL of 3600 seconds (1 hour). This means DNS resolvers will cache the record for an hour before checking for updates, balancing performance with flexibility.