needed, necessary

need, necessity

(mathematics) vector / (computer science) vector (a one-dimensional array) / (figuratively) direction (in life)

question, problem on homework etc. / a question; a matter (of time etc.) / a problem (something that needs to be dealt with); a trouble / an issue; a matter

zero COVID (having zero COVID-19 cases)

Short for プラスマイナスゼロ (purasu mainasu zero).

(linear algebra) column vector

(linear algebra) row vector

a zero vector

impossible to understand, utterly confused