Max Webber's definition:
Power is the ability to accomplish aims despite the resistance of others. Power may be deprived from a number of sources. It may come from sheer physical force or from the use of economic resources.

Two Types of Power
Legitimate powerPower you can reasonably claim to have a right to use. Used by elected official and is often referred to as authority.
Illegitimate Power
Power that you cannot reasonably claim to have a right to use. Requires the use of coercion, violence or force. It is not recognized by society some examples include terrorism.

Forms of Power
New/social media
Labour
Demonstration, e.g. Riots or petitions.
Financial
Law and Policy

Access to Power
To those with power, it is easier to create social change. Social movements with greater access to power are more likely to achieve social change. Groups and induvial with great power are more able to resist the efforts of social movements with lesser power.