  Matrix product codes are generalizations of some well-known constructions of
codes, such as Reed-Muller codes, $[u+v,u-v]$-construction, etc. Recently, a
bound for the symbol-pair distance of a matrix product code was given in
\cite{LEL}, and new families of MDS symbol-pair codes were constructed by using
this bound. In this paper, we generalize this bound to the $b$-symbol distance
of a matrix product code and determine all minimum $b$-symbol distances of
Reed-Muller codes. We also give a bound for the minimum $b$-symbol distance of
codes obtained from the $[u+v,u-v]$-construction, and use this bound to
construct some $[2n,2n-2]_q$-linear $b$-symbol almost MDS codes with arbitrary
length. All the minimum $b$-symbol distances of $[n,n-1]_q$-linear codes and
$[n,n-2]_q$-linear codes for $1\leq b\leq n$ are determined. Some examples are
presented to illustrate these results.
