Bicollared

A Subset $X\subset Y$ is said to be bicollared in $Y$ if there exists an embedding $b:X\times [-1,1]\to Y$ such that $b(x,0)=x$ when $x\in X$. The Map $b$ or its image is then said to be the bicollar.

References

Rolfsen, D. Knots and Links. Wilmington, DE: Publish or Perish Press, pp. 34-35, 1976.