What is Accountability?

Legal Definition
In ethics and governance, accountability is answerability, blameworthiness, liability, and the expectation of account-giving. As an aspect of governance, it has been central to discussions related to problems in the public sector, nonprofit and private (corporate) and individual contexts. In leadership roles, accountability is the acknowledgment and assumption of responsibility for actions, products, decisions, and policies including the administration, governance, and implementation within the scope of the role or employment position and encompassing the obligation to report, explain and be answerable for resulting consequences.

In governance, accountability has expanded beyond the basic definition of "being called to account for one's actions". It is frequently described as an account-giving relationship between individuals, e.g. "A is accountable to B when A is obliged to inform B about A's (past or future) actions and decisions, to justify them, and to suffer punishment in the case of eventual misconduct". Accountability cannot exist without proper accounting practices; in other words, an absence of accounting means an absence of accountability.

Accountability is an element of a RACI to indicate who (or group) is ultimately answerable for the correct and thorough completion of the deliverable or task, and the one who delegates the work to those responsible.

There are various reasons (legitimate or excuses) why accountability fails.
-- Wikipedia
Legal Definition
When one party must report its activities and take responsibility for them. It is done to keep them honest and responsible.