parallel在英语中的比喻义如何理解？

Y.LuffyUID: 2996786

我们说两个事物的发展parallel是什么意思？

苏梳眠UID: 2717864

MW上的解释~
parallel
1 a : extending in the same direction, everywhere equidistant, and not meeting  *parallel rows of trees*  b : everywhere equally distant  *concentric spheres are parallel*
2 a : having parallel sides  *a parallel reamer*  b : being or relating to an electrical circuit having a number of conductors in parallel  c : arranged in parallel  *a parallel processor*  d : relating to or being a connection in a computer system in which the bits of a byte are transmitted over separate channels at the same time  *a parallel port* ? compare SERIAL
3 a (1) : similar, analogous, or interdependent in tendency or development  (2) : exhibiting parallelism in form, function, or development  *parallel evolution*  b : readily compared  : COMPANION  c : having identical syntactical elements in corresponding positions;  also   : being such an element  d (1) : having the same tonic -used of major and minor keys and scales  (2) : keeping the same distance apart in musical pitch
4 : performed while keeping one's skis parallel  *parallel turns*