chevet
it is called the ambulatory.
Choir or transept.
king john
in the tabernacle behind the altar.
People visiting pilgrimage churches often wanted to walk around the church and observe the architecture. After walking down one side aisle, they would walk in front of the altar to amble down the other side aisle. Oftentimes this was disruptive to an ongoing church service. Ambulatories provide a pathway around the back of the altar for visitors to walk across covertly. Pilgrimage churches usually implemented this design to accommodated the large influx of people they anticipated would be walking through the church.
Why didn't Prince William watch his bride walk down the aisle? Tradition. The groom is the last person to see the bride, and can only do so after she has completed the long walk down the aisle and is at his side. Since the aisle at Westminster Abbey is about 300-feet long, he had at least a four-minute wait at the altar.
A Reredos.
Consecrated Hosts are stored in a locked Tabernacle, not on the altar. The Tabernacle may be located immediately behind the main altar or on its own pedestal in the Church, non on the altar.
The walkway between pews in a church is called an aisle. The wedding party and bride walk down the aisle to the front of the church. (The groom can enter from any door. He does not walk down the aisle in a formal procession, but waits at the altar for his bride.) However, other weddings not in church do not use a structural "aisle". They might place a "runner", often made of satin, across a lawn to create an "aisle" between chairs for seating.
I think that you are asking about the ceremony, in which case, the groom waits for the bride at the end of the aisle along with the officiant, that is, in front of the altar, etc. The bridesmaids will come down the aisle first, followed by the bride to join her groom with the officiant.
There are 9 chapelsCrypt ChapelsBethlehem ChapelChapel of St. Joseph of ArimatheaResurrection ChapelGood Shepherd ChapelNave ChapelsSt. Mary's ChapelSt. John's ChapelChildren's ChapelHoly Spirit ChapelWar Memorial ChapelThe High Altar (in the chancel/sanctuary to the east of the great choir) is considered the altar for the entire nave and not a chapel unto itself.The Cathedral's nave bays do not contain altars, and so we do not count them as chapels.
Tiaria said its called the pulpit