Whats does "hr" mean among "V" and "Ah" in batteries?

It means that the battery has a capacity of 25 Ah when discharged in 10 hours. 25 Ah is 25 Amps for 1 Hour which is equivalent to 2.5 Amps in 10 Hours.

So if you load the battery with 2.5 Amps it will last 10 Hours.

If loaded with a higher current usually battery capacity decreases so that is why the 10 Hours is mentioned, it results in a higher battery capacity making the battery look "better".

How many watts: simple 2.5 Amps x 12 V = 30 Watts and that for 10 Hours.

I concur with what others have said above. Battery capacity is somewhat dependent on discharge current At higher discharge current, the battery capacity decreases.

Here are discharge curves that illustrates this. The same battery was discharged at different rates.

( source )

This chart is for a Li-ion battery. A chart for a Lead-acid battery would also show the decrease in capacity.

Note that in this case, C doesn't stand for °Celsius. In the chart above, C stands for discharge rate normalized by battery capacity. 1C means such rate that will discharge a battery in 1 hour. 0.5C and 4C correspond to 2 hours and 15 minutes, respectively. Consider a 12Ah battery. For such battery 0.5C, 1C, 4C correspond to 6A, 12A, 48A, respectively. This kind of normalization helps to abstract away the size of the actual battery, which makes it easier to look at other aspects. (More here.)

update: Here's another similar chart.

The capacity of a battery depends partly on how fast you discharge it. A specification like "25Ah/10hr" says that the battery has a capacity of 25 amp-hours when it is discharged at a rate that takes it from fully charged to fully discharged in 10 hours — in other words, at \$\frac{25Ah}{10 hr} = 2.5 A\$.