What is the difference between "soft money" and "hard money" campaign donations

Campaign finance in the United States is the financing of electoral campaigns at the federal, state, and local levels. At the federal level, the primary source of campaign funds is individuals; political action committees are a second source. Contributions from both are limited. These regulated donations are often referred to as "hard money." Corporations and unions are prohibited from contributing directly to a candidate's campaign. "Soft money" are funds spent by organizations that are not contributed directly to candidate campaigns, and which do not "expressly advocate" the election or defeat of a candidate. Public funding is available for Democratic or Republican presidential candidates during the election campaigns during both the primaries and the general election. Eligibility requirements must be fulfilled in order to qualify for public funding and those that do accept public funding are subject to spending limits. Races for state and local offices operate under the laws of their jurisdictions. Over half the states allow some level of corporate contributions. Some states have limits on contributions from individuals that are lower than the national limits, while others have no limits at all. These state rules apply to races for state and local offices. Campaign finance is a controversial issue, pitting concerns about free speech as an argument against legal restrictions against concerns about corruption and inequality on the part of those who favor existing or further restrictions.

Hard money - is from political donations that are regulated by law through the Federal Election Commission. Soft money - is money donated to political parties in a way that leaves the contribution unregulated. (sorry I couldn't found other nice explanation)