What is it?

[Marc]

It's a rapier.
Spanish or Italian, more probably the former, although the quillion and knuckle bow finials are not of the most typical forms for such provenance. End of the 17th - beginning of the 18th centuries, with the blade totally developed in a purely thrusting form, that later on, and after some evolution, would be characteristic of the smallswords. In fact, at that time, it already was the rage in some places in Europe, namely France, but the smallsword fashion meet some resistance in its introduction in Spain, for a number of reasons.

It's in quite a sad condition... the hilt would have been of the so-called "cup-hilt" form, but it's lacking the actual "cup" that gives name to the type (see my avatar picture for an example of a very decorated, very Spanish and somewhat earlier variety).

But, anyway... the ricasso is quite skinny, somewhat "underdeveloped" for the period and the kind of fencing these swords were built for, which makes me somewhat suspicious that the blade could in fact not belong to the hilt and be of a later date. This would ask for a closer inspection, of course, before saying anything with a good degree of certainty, but it's something worth mentioning. It doesn't fall into the realm of impossibility, though.

By the way, just as a trivia note, the actual bullfighter swords are in fact a specialized evolution of this 17th century civilian swords, that were actually used to kill bulls in public displays of courage/foolishness.

Marc