No. “No deal” occurs if we fail to agree a withdrawal agreement with the EU before we officially leave the EU on 29 March next year. The transition period is part of the withdrawal agreement, so if we leave the EU with no deal, that means no withdrawal agreement, and therefore no transition period.
The transition period is the time between the day we officially leave the EU (29 March 2019) and December 2020 (although it could be extended to 2021 or 2022). During the transition period, we will trade with the EU as we do currently.
The transition period will be used to try and negotiate that future relationship deal with the EU. The withdrawal agreement is not the same thing as the future relationship deal.
The plan is for that future relationship deal to kick in when the transition period ends.
This article is part of our Ask Full Fact series on Brexit, answering your questions about Brexit and the latest negotiations between the UK and the EU.