noun
periodic commuting fee; commuting expenses
Often refers to a monthly or regular pass cost for employee travel, or the allowance paid by a company.
会社が定期代を支給してくれる。
The company pays my commuting expenses.
今月の定期代はいくらですか。
How much is the monthly commuter pass fee this month?
交通費 is a broader term for all transportation expenses, not limited to regular commuting.
Compound of 定期 (fixed period) and 代 (fee, charge).