In the case of roads, a real world tunnel is a constructed passage that allows you to pass directly from A to B instead of taking a route that is longer and/or has more things to slow you down. Examples include tunnels through mountains that you might otherwise have to go round, underpasses that let you get to the other side of the road without walking across it, and subway tunnels that let trains move around a city without contending with roads and buildings.

In each of these cases, a tunnel provides a direct path that avoids some type of complexity you'd otherwise have to deal with, in networking it is used in the same way.

An IPv4 over IPv6 tunnel allows IPv4 to pass through an IPv6 network into another IPv4 network, something that would otherwise not be possible without the originating computer understanding the IPv6 network.

A VPN is a tunnel specifically intended for connecting two private networks without the overhead of translating the IP addresses between private and public addresses at each end.

An example that combines the two is game VPN software like Hamachi that could be used to play over the internet games which used old protocols like IPX or relied on local discovery to find other players.

In the case of roads, a real world tunnel is a constructed passage that allows you to pass directly from A to B instead of taking a route that is longer and/or has more things to slow you down. Examples include tunnels through mountains that you might otherwise have to go round, underpasses that let you get to the other side of the road without walking across it, and subway tunnels that let trains move around a city without contending with roads and buildings.

In each of these cases, a tunnel provides a direct path that avoids some type of complexity you'd otherwise have to deal with. In networking it is used in the same way.

An IPv4 over IPv6 tunnel allows IPv4 to pass through an IPv6 network into another IPv4 network, something that would otherwise not be possible without the originating computer understanding the IPv6 network.

A VPN is a tunnel specifically intended for connecting two private networks without the overhead of translating the IP addresses between private and public addresses at each end.

An example that combines the two is game VPN software like Hamachi that could be used to play over the internet games which used old protocols like IPX or relied on local discovery to find other players.

In life a tunnel passes through an area that is otherwise impassable, in networking it is used in the same way.

An IPv4 to IPv6 tunnel allows IPv4 to pass through an IPv6 network into another IPv4 network, something that would otherwise not be possible without the originating computer understanding the IPv6 network.

In the case of roads, a real world tunnel is a constructed passage that allows you to pass directly from A to B instead of taking a route that is longer and/or has more things to slow you down. Examples include tunnels through mountains that you might otherwise have to go round, underpasses that let you get to the other side of the road without walking across it, and subway tunnels that let trains move around a city without contending with roads and buildings.

In each of these cases, a tunnel provides a direct path that avoids some type of complexity you'd otherwise have to deal with, in networking it is used in the same way.

An IPv4 over IPv6 tunnel allows IPv4 to pass through an IPv6 network into another IPv4 network, something that would otherwise not be possible without the originating computer understanding the IPv6 network.

A VPN is a tunnel specifically intended for connecting two private networks without the overhead of translating the IP addresses between private and public addresses at each end.

An example that combines the two is game VPN software like Hamachi that could be used to play over the internet games which used old protocols like IPX or relied on local discovery to find other players.