An HDHP is a High Deductible Health Plan that has higher deductibles than a traditional health plan. Therefore, you would typically know you have an HDHP by the amount of the deductible. See the amounts below. And, an HDHP can be combined with an HSA (Health Savings Account) which allows one to pay for certain medical expenses with money free from federal taxes.
The IRS defines a high deductible health plan as any plan with a deductible of at least $1,350 for an individual or $2,700 for a family. An HDHP’s total yearly out-of-pocket expenses (including deductibles, copayments, and coinsurance) can’t be more than $6,650 for an individual or $13,300 for a family. (This limit doesn't apply to out-of-network services.)
More information can be found on healthcare.gov --
https://www.healthcare.gov/glossary/high-deductible-health-plan/
