see caption
Shaded area is the transept; the darker shaded area at the centre is known as the crossing
Wikimedia Commons

The transept is the part of a Christian church crossing the area between the naveCentral part of a church, used by the laiety. and the chancelPart of a church containing the altar, used by the officiating clergy. at right angles, forming a characteristic cruciform shape. Trransepts began to be introduced into Western church architecture in about the 5th century, and often provided space for additional chapels.[1] As the altar is usually at the eastern end of a Christian church, the transept extends to the north and south.[2]

The term is also used more generally to describe any significant part of a building lying at right angles across the structure’s main axis.[3]

References

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Bibliography

Clarke, Michael. “Transept.” The Concise Oxford Dictionary of Art Terms, Online, Oxford University Press, 2010, https://www.oxfordreference.com/view/10.1093/acref/9780199569922.001.0001/acref-9780199569922-e-1691.
Curl, James Stevens, and Susan Wilson. “Transept.” Dictionary of Architecture and Landscape Architecture, Online, Oxford University Press, 2015, https://www.oxfordreference.com/view/10.1093/acref/9780191918742.001.0001/acref-9780191918742-e-4769.
Jones, Tom Devonshire, et al., editors. “Transept.” Oxford Dictionary of Christian Art and Architecture, Online, Oxford University Press, https://www.oxfordreference.com/view/10.1093/acref/9780199680276.001.0001/acref-9780199680276-e-1799.