Obon is a traditional Japanese custom to honor the departed but these days it seems to be more of a family reunion where folks living in the main cities travel back to other areas of Japan to see their folks.
The Obon period starts today (12th August) and finishes at the end of this week (16th August). Most traditional Japanese companies will close their offices like Good Smile Company but many retail and foreign capital companies (Gaishikei) will continue with business as usual. Employees would then have to use up their paid holiday quota if they wanted time off. At Amazon or Microsoft, we didn't get any Obon time off.
Obon is the main reason why the trains are so empty and many parts of Tokyo seem so deserted right now.
The phrase "Kisei Rush" [帰省ラッシュ] is used to describe the hordes of folks rushing back to see their folks who are situated outside Tokyo or other major cities.
The news clip below talking about the Kisei Rush. Japan now has the 1000 yen highway deal where one can travel as much as they want which can cost in the 10000's. The 1000 highway deal "1000 yen Kousoku" [1000円高速] clogs up the highway even more and while the news item shows tailbacks for 14 kilometers, they can go up to 43 kilometers or so.
Most of the Shinkansen (bullet train) seats are booked but there are a certain number of standing places too. Most of the domestic flight seats are also booked. Probably not a great time to visit Japan if one plans to travel around.
Listen to the video and see if you can pick out the words "Kisei Rush."
And then towards the end of the week, their air and roads are clogged with folks trying to get back to Tokyo and other major cities.
I've seen some news in Korean too and see that they have something similar where folks in Seoul rush back to see their folks during particular seasons.
Image from Sankei and Wikipedia has more info about the Obon tradition.