Originally a military term for the rear unit or rearguard. Now also used figuratively for the last person or thing in a sequence.
He served as the rear guard of the procession.
I run at the very back in the marathon.
anchor; last person
Used in sports or group activities for the person who goes last, such as the anchor leg in a relay or the final performer.
The anchor of the relay is the fastest runner on the team.
It was the veteran soldier who served as the rear guard for the retreating troops.
He was running last in the marathon, but he never gave up until the end.
In the climbing party, it's arranged that the person with the most stamina takes the rear position.
アンカー is a casual loanword for the last runner in a relay or last player in a lineup, matching the sports sense of 殿（しんがり）but without its older military feel.
殿（しんがり）meaning rear guard is written with the same kanji as 殿（どの）, the polite honorific suffix attached to names, but the two are unrelated in meaning.
rear guard; rear guard unit
Standard kanji spelling for this word.
Kana spelling is common when the kanji 殿 might be misread as との or どの.
The reading しんがり is a compound of しん (rear) and がり (guard). The kanji 殿 is used for its meaning of 'rear' or 'back' in this context.