Domestic travelが国内[旅行](https://eikaiwa.dmm.com/uknow/questions/44579/)と言う意味となります。
例：
Domestic travel has been picking up lately.
最近、国内旅行が活発化しています。
travel domestically と言うこともできます。「国内を旅行する」という意味になります。
例：
I like to travel domestically as well as internationally.
私は国内を旅行するのも国外を旅行するのも好きです。
A "What are you doing for the summer holidays?"
B "I'm staying local. Just doing a journey around Japan with my wife."
A "We did a domestic trip last year. It was great!"
B "But we're going abroad this year - to Australia."
A "Nice!"
A domestic flight is a flight that does not leave national territory.
A「[夏休みに](https://eikaiwa.dmm.com/uknow/questions/70537/)何をするんだい？」
B「私は[地元](https://eikaiwa.dmm.com/uknow/questions/44761/)にいるさ。妻と一緒に日本を旅をしているよ。」
A「昨年、国内旅行をしました。素晴らしかったよ！
B 「今年はオーストラリアに行くんだけどね。」
A 「すてきやん！」
A domestic flightは国内線をさします。
If you are flying from one part of the country to the other it can be referred to as a Local or Domestic trip/flight.
You can say you are traveling "locally".
Flying within the same country is called a "domestic/local/national flight, it is when we are not travelling to foreign or international countries.
"I do a lot of domestic travel!"
"I live in Tokyo and I have to fly to Hokkaido for a meeting, it's just a local flight."
"I don't travel abroad a lot, but, I do a lot of national travelling!"
同じ国でのフライトはdomestic/local/national frightと呼ばれ、海外,海外の国には行かない旅行のことです。
例
"I do a lot of domestic travel!"
"私は国内旅行をたくさんしています！"
"I live in Tokyo and I have to fly to Hokkaido for a meeting, it's just a local flight."
"私は東京に住んでいて、北海道にミーティングに行く必要があります。ただの国内便です。"
"I don't travel abroad a lot, but, I do a lot of national travelling!"
"私は海外旅行はしませんが、国内の旅行をたくさんしています！"
We're not going abroad we're doing the local sights
I'm staying home
Often when we are travelling in our own country we use very informal language to indicate we are not taking an overseas trip - so it is usual to express it in the negative form.
"I intend to travel locally."
This means you will be traveling within your country/within a specific area/within Japan'
"I will travel within the country.' and "I will travel nationally." mean that you will be travelling only in Japan and will not be going abroad.
"I intend to travel locally."
This means you will be traveling within your country/within a specific area/within Japan'
「近場を旅行するつもりです。」
これは、国内またはある地域内で旅行するという意味です。
"I will travel within the country.' and "I will travel nationally." mean that you will be travelling only in Japan and will not be going abroad.
Travel withing the countryとTravel nationallyは、どちらとも日本国内で旅行をし、海外へは行かないと言う意味です。
日本 
イギリス 
南アフリカ 
