Alphabet Inc. (GOOGL) is having a good week. The stock is trading higher on Wednesday, up about 5% in just three days. But the real question is whether this rally has legs — and the answer might come down to a single price level.

Alphabet is what traders call a Stock of the Day because it's testing resistance, and that test could determine whether the uptrend continues or fizzles out.

Let's back up. Resistance is just a fancy term for a price where a lot of people want to sell. When a stock is trending higher, it's because there aren't enough sell orders to fill all the buy orders. Buyers have to outbid each other, pushing the price up. But at resistance, there are suddenly enough sellers to satisfy demand, so the rally stalls — or at least takes a breather.

Here's the interesting part: resistance often forms at levels that used to be support. Take a look at Alphabet's chart. Back in April, the $374 level was support — a price where buyers stepped in and the stock bounced. People who bought there felt good when the stock went higher. But then in early June, that support broke. Suddenly, those same buyers regretted their purchase. Some decided they'd sell if they could get back to breakeven. So when Alphabet rallied back to $374, they placed sell orders. That turned old support into new resistance.

The same thing is happening right now at the $358 level. That was support in early June. Now it's resistance, thanks to buyers' remorse. People who bought at $358 are now selling, creating a wall of supply.

If Alphabet can push through $358 and stay above it, that's what traders call a breakout. It's a bullish signal because it means the sellers who created the resistance are gone — they've either canceled their orders or finished selling. Once that overhead supply clears, buyers may once again have to outbid each other to attract sellers. That could keep the uptrend intact.

So keep an eye on $358. If Alphabet breaks out, the rally could have room to run. If it stalls, well, resistance did its job.