Roble is a commonly-seen but non-standardised Spanish labelling term indicating that the wine has been aged in barrel for a period that is less than that required locally to gain the starter Crianza designation, which is used for the youngest official category of oak-matured wine.
In the Spanish ‘hierarchy’ of wines, the ageing / quality ladder runs: Joven / Tinto (young, little or no oak ageing) -> Roble (some oaking) -> (moving onto the three legally-controlled terms) Crianza -> Reserva -> Gran Reserva.
So basically, Roble wines have seen a little bit of oak (less than twelve months anyway) and should present as young and fruity but with a bit of added weight, spice and interest from the wood. Similar terms to Roble include Semi-Crianza (which is slightly misleading as it conflates a legally-controlled term with an unregulated one) and the self-explanatory x meses en barrica (x months in barrel).
With 90% of Spanish blancos and rosados being totally unoaked, the whole Crianza / barrel ageing system as outlined above refers overwhelmingly to red wines and, in particular, to those coming from blue-chip DOs Rioja and Ribera del Duero.