Spread is the difference between the price at which something can be bought and the price at which it is sold. In trading the buy price is often called the ask price, the selling price is often called the bid price: sometimes therefore the spread is called the bid-ask spread.
In forex trading, if you want to take a long position in e.g. AUD/USD, you would need to pay 0.6755. If you wanted to close that position immediately, you would receive 0.6754. So the spread is 0.0001: this is also called 0.0001 on this pair is 1 pip.
But be aware that the spread changes through the day. It will not often get narrower than 1 pip for AUD/USD but it will get wider, such as when large markets like London and New York are about to close or have just opened, or when news relating to the AUD or the USD is coming out.
A wider spread makes it harder to make a profit - right now price only need to move 1 pip in order for your purchase of AUD/USD to break even, and 2 pips for it to start making a profit. But of the spread is 8 pips, then price would need to move 8 pips for you to break even. Wide spreads are more common when there is not much trading activity going on which makes breaking even then even harder.