Literally 地道 means tunnel, subway, or underpass. There was a classic movie called 地道战 (the War in the Tunnel) , which was about the story of Chinese soldiers and farmers dug tunnels underground to fight the Japanese invaders in the 1940s.
But in our daily conversation, 地道 has quite a few different interesting usages. Let's see some examples:
She speaks perfect mandarin.
His work is really well-done.
In above sentences, 地道 means perfect, or skill up to standard.
The food in that Chinese restaurant is really authentic.
In this sentence, 地道 means authentic.
This is genuine Longjing tea.
Here, 地道 means from the place well-known for a certain product;
That person is not an honest one. He cheated.
In this sentence, 地道 means honest, obey the common moral rules.