English: Spanish labels. Definitions as in APWeb glossary and Simpson (2005, 2010) Plant Systematics glossary.

APWeb (Reference: http://www.mobot.org/mobot/research/apweb/top/glossaryi_p.html#P):

gynoecium: collectively the carpels of a flower

pistil: a free carpel or a group of fused carpels, a rather confusing term; also as pistillode, a sterile pistil, often rudimentary - a more useful term.

Simpson (2005) Plant Systematics:

Gynoecium refers to all female organs of a flower.

A pistil is that part of the gynoecium composed of an ovary, one or more styles, and one or more stigmas. (...) Pistils or ovaries may be simple, composed of one carpel, or compound, composed of two or more carpels. By convention, if there is more than one ovary, style, or stigma, but if any of these appear fused in any way (e. g. three apparent ovaries fused at the base), they are all part of the same pistil. (One unique case are the Asclepiadoids, in which the gynoecium consists of two carpels made up of two distinct ovaries and styles but a single stigma joining the styles, because the stigmas of the two carpels are connate, the whole structure is termed a single pistil).

Flower images modified from these ones: http://www.anbg.gov.au/glossary/webpubl/ovpositi.jpg