Wine corks are, of course, corks made from the bark of the cork tree.
More recently there have been attempts to create technological substitutes for cork, including using screw tops and plastic corks, but these attempts have so far met with substantial resistance by consumers.
There is a need for an alternative - the world's supply of cork is relatively small. Also, being organic, cork is susceptible to mould growth which can affect the flavour of the wine, causing it to become corked. Wine corks also deteriorate with age, and can dry, become crumbly and stop sealing the bottle properly.
For all of these reasons it seems likely that one solution or another will eventually achieve consumer acceptance. Most likely this will be the use of plastic corks which are starting to be a regular feature of low to medium priced wine, with premium wine continuing to use real cork.
Some pundits suggest that real cork is better for the wine because it can still breathe slightly, allowing fermentation and other processes to continue to some degree. Research continues towards a non-cork which will also provide this characteristic.
If you plan to store wine for a long time, you should lay the bottles on the side to ensure the cork does not dry out.