Silicic implies that the rock is relatively high in silica, and for igneous rocks this includes granites, diorites, rhyolites, dacites, and a bunch of others. On the other hand, mafic rocks are relatively low in silica, and include basalts, gabbros, basaltic andesites, and in some folks' minds, andesites as well. The high viscosity means that the magma or lava can effectively plug up the conduit and allow high gas pressures to build up. This leads to explosive eruptions. This can produce widespread ash falls as well as pyroclastic flows.
Mafic magmas are much less viscous.
This means that they can migrate more easily through the volcanic plumbing, and they are not very effective at plugging up the conduit. Basaltic eruptions may involve spectacular lava fountains, but these are not really explosions. Of course once mafic lava is on the surface, it flows very easily. I hope this has helped to answer your questions.