data1 = {a,b,c,d,e};
data2 = {s,t,u,v,w};

(*MapThread correctly calls f[a,s], f[b,t], but builds up an expression*)
MapThread[f, {data1, data2}]

(*MapIndexed calls g[a,{1}], g[b,{2}], but builds up an expression*)
MapIndexed[g, data1]