Answer
${HCO_3}^-$ is a weak base.
Conjugate acid: $H_2CO_3$, which is a weak acid.
Work Step by Step
${HCO_3}^-(aq) + H_2O(l) --> H_2CO_3(aq) + OH^-(aq)$
Since $H_2CO_3$ is the $H{CO_3}^-$ after receiving one proton, it is the conjugate acid.
Since $H{CO_3}^- $ is a weak base (but not insignificant), his conjugate acid will be weak too.