I'm assuming that "moral concept" means concept in morality, ethics? What does it mean for any concept (let alone Ownership) to be moral, but NOT legal? Please explain the sentences in bold at a high school level?
1.4.3 ESTATES IN LAND
A second aspect to the land law logic which must be internalised, and which again is difficult (partly due to terminology), is the idea of estates in land rather than ownership of land. To understand land law it is essential to get rid of the idea of ownership of land. There is no such thing as ‘the owner’ of a piece of land in English and Welsh land law. This does not mean that people are lying when they say they own their land, nor does it mean they are being inaccurate as such. This book will refer to landowners and owners of land. It is not that this term is wrong, it is that is [sic] has no legal definition. There is no legal concept of ownership, although of course there is a moral concept [emphasis added], and indeed the term is used as a shorthand for one or more concepts which do have a legal meaning—such as freeholder, leaseholder, owner of the freehold title, and registered proprietor. To a certain extent, all of these terms means ‘owner’, although not ‘the owner’.
Emma Lees, The Principles of Land Law (Oxford University Press, 2020), page 20.