what is a random walks mean reverting level and covariance stationary?

Random walks mean reverting level is a continuous process in which the current or expected value of a given asset or market is governed by the mean of its previous values (the long-term average). It is assumed that the asset or market will tend to move toward its mean or toward some other long-term time-averaged value over time. Covariance stationarity is an assumption made in the study of stochastic processes. It is the assumption that information about the mean, variance and covariance of a process is invariant over time, and independent of any particular point in the process. This means that covariance of a process is not affected by a change in time origin. Covariance stationarity implies that the expected value of a process remains constant over time and that the actual variations depend only on the time differences between the values.