I'm afraid the numbers above bars are just called... "bar numbers". They serve as an index so that you can communicate about places in a score when there is no opportunity to point to them. For instance, a scholar would write that the development section begins "in bar 156", or a conductor would instruct the orchestra players "We'll take it from bar 135". (In practice, for orchestral scores you'd give section numbers instead, since the bar numbers in symphonic scores get rather high.)
This are bar numbers, one possibility of orientation for rehearsals. (Sometimes as here they are written at the beginning of each line, sometimes in regular distance as every multiple of 5 or 10.)
Other possibilities are rehearsal marks (see this related question), either big capitals (starting with A, mostly I is omitted in favour of J) or numbers (starting from one) in a circle or a box at distinct positions, as key signature change, or in appropriate distance.