It is a Proprietary Score that Marketo assigns from 0 - 100.
Understanding the Engagement Score - Marketo Docs - Product Docs
I'm not sure anyone uses this score for anything. It indicates how well your content resonates.
But, you do not "get these leads". There may be a filter constraint on Engagement score, but I'm pretty sure this is not available.
Like Josh mentioned, you can't "get leads" from the engagement score. Were you hoping to use your "engaged" leads in another campaign? If so, you can create a smart list that looks for leads who completed whatever activities you would like to use in another campaign. For example, you can use the leads who clicked the primary CTA link in this email to target in another campaign.
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