What does this mean?

Headline from USA Today "Iran reacts "positively" to US-European offer"

Now what in the world does this mean?

Iran said Tuesday that it is ready for "serious negotiations" as Tehran gave its long-awaited reply to a joint U.S.-European offer aimed at ending the standoff over the country's nuclear research program.
Ali Larijani, Iran's top nuclear negotiator, said Tehran had responded "positively" to the Western offer, but he refused to say whether Iran would comply with the key demand: suspending its uranium enrichment program.