It is a measurement of expected profits or losses over the long term. A positive expected value (+EV) will provide long-term profits. A negative expected value (-EV) will provide a long-term loss. We could flip a coin for hours, and neither of us would have an advantage. That's because we have half a 50-50 chance of losing and half a 50-50 chance of winning. There may be fluctuations back and forth, but as long as we flip the coin many times, we will both be at breakeven. This bet has a neutral expected value.
Suppose for example you don't like flipping a coin anymore and want to end the game. Your friend offers a deal to keep you in the game. In the updated deal, you win $1.10 for the head and lose $1 for the tails. Half the time you will win $1.10 and half the time I will lose $1. If you and your friend flip the coin 100 times, you will get an average of 50 wins ($55) and 50 losses ($50). Now the expected value of the bet is positive.
Every bet in sports betting has a negative or positive expected value. In rare cases, the expected value is neutral. When it comes to sports betting, the trick is to find a positive expected value and avoid a negative one.
The expected value can be calculated using the following formula:
(bet win amount probability of winning) - (bet lose amount probability of losing).
Let's apply the coin toss option. The amount won will be 1.10 half the time or 0.5. Subtract from this the amount lost on the 1.00 half the time bet or 0.5.
(1.10*.5)-(1.00*.5)=.05
So, on average, your friend should expect a profit of 5 cents on every dollar bet. The EV calculation can be tricky. And the "probability of winning and losing" is the challenging part. There are many sites that try to help you with this.
Coinmarketcap
CoinGecko
DEXTools