This arises from the Ley de Propiedad Horizontal (LPH), Article 18.2 as amended in 1999, on the rights of members of a an owners' association to challenge resolutions of the association in court:

"Estarán legitimados para la impugnación de estos acuerdos los propietarios que hubiesen salvado su voto en la Junta, los ausentes por cualquier causa y los que indebidamente hubiesen sido privados de su derecho de voto"
https://www.iberley.es/legislacion/ley-propiedad-horizontal-...

The provincial courts (audiencias) have been confused by this use of the expression "que hubiesen salvado su voto" and have adopted contradictory interpretations of what it means. Basically, some have ruled that "salvar el voto" means voting against the motion and having your opposition explicitly recorded in the minutes. Others have ruled that it simply means the same as voting against the motion.
https://www.abogadoarrendamientos.com/que-significa-salvar-e...

In both cases, it's interpreted as a vote against, which is what the expression means in business contexts, for example: a dissenting vote:
https://www.proz.com/kudoz/spanish-to-english/law-patents/48...

However, this case law from the provincial courts has been superseded by a Supreme Court judgment of 2013, which explicitly rejects the conclusions of the provincial courts and establishes the legal meaning of the term.

Those who vote against a resolution can subsequently challenge it legally, if the other requirements for doing so are met. But "salvar el voto" is not synonymous with voting against, otherwise (the judgment argues) the legislator would not have introduced it into the law. The crux of the issue is set out in the following paragraph:

"La necesidad de salvar el voto únicamente tiene sentido en aquellos casos en los que los propietarios asisten a la Junta sin una información o conocimiento suficiente sobre el contenido y alcance de los acuerdos que se van a deliberar, y deciden no comprometer su voto, favorable o en contra, sino abstenerse de la votación a la espera de obtenerla y decidir en su vista. A ellos únicamente habrá de exigírseles dicho requisito de salvar el voto, pues en otro caso sí que se desconocería su postura ante dicho acuerdo. Con ello se evitaría, además, que el silencio o la abstención puedan ser interpretados como asentimiento al posicionamiento de la voluntad mayoritaria que se expresa en uno o en otro sentido."
https://www.abogadoarrendamientos.com/que-significa-salvar-e...

In other words, it's a vote that reserves the voter's position in situations where the member considers that he/she does not yet have sufficient information to vote yes or not. If, once the position is clarified, the member is in favour, obviously he/she will not legally challenge the resolution. But the member reserves the right to challenge the resolution if, once the position is clarified, that member opposes it. So it is, in effect, a kind of abstention that reserves the right to oppose the resolution. An abstention per se is interpreted as consent to the majority decision and rules out the possibility of a subsequent legal challenge by the abstainer. (This, of course, is why "salvación de voto" and "abstención" are listed separately in your document.)

So in the light of this I think the right expression is a reserved vote. Here's an example of this expression (in a different context):

"a member may reserve a vote until the member has taken further advice in respect of the matter"
http://archive.treasury.gov.au/documents/495/pdf/corporation...

Case law on the subject, and the Supreme Court's ruling, are also explained here, along the same lines as in the source I've cited:
https://www.iberley.es/temas/impugnacion-acuerdos-junta-prop...

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Note added at 2 hrs (2019-04-01 14:46:26 GMT)
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I've been a member of a "comunidad de vecinos" for over twenty years and I've never heard of this before. I wonder whether our admnistrators are even aware of it. I feel like bringing it up at the next meeting.