p-values in mixed model

[elroy]

I'm a little confused as to how to interpret the p-values in the model below, under "Fixed effects." I had two fixed effects (group and condition), group with three levels and condition with two. The three groups are EN, HS, and SB, and the two conditions are EN-GJT-R-GAP and EN-GJT-R-RES.

Under "Fixed Effects," I'm not sure what (Intercept) refers to? I thought the estimate referred to a difference between each parameter and the first one alphabetically (the one listed as (Intercept)), but here I have two different fixed effects, so does (Intercept) refer to groupEN or conditionEN-GJT-R-GAP? How could it simultaneously refer to both? And what do the estimates for groupHS, groupSB, and conditionEN-GJT-R-RES refer to? Also, what does the p-value for (Intercept) refer to? I thought that for the other ones (not (Intercept)), the p-values indicate the statistical significance of each parameter vis-à-vis the (Intercept), but again, how can this work if there are two different parameters the (Intercept) could refer to, and what does the p-value of the (Intercept) refer to if it's not being compared to anything else? Clearly I'm missing a lot of things, so any help would be vastly appreciated!

Linear mixed model fit by REML. t-tests use Satterthwaite's method ['lmerModLmerTest']
Formula: score ~ group + condition + (1 | subject) + (1 | token_set) +      (1 | list)
   Data: EN_JT_1

REML criterion at convergence: 521.2

Scaled residuals: 
    Min      1Q  Median      3Q     Max 
-3.4748 -0.3124  0.2425  0.6686  1.8308 

Random effects:
 Groups    Name        Variance  Std.Dev. 
 subject   (Intercept) 2.170e-02 1.473e-01
 token_set (Intercept) 3.147e-03 5.610e-02
 list      (Intercept) 1.319e-10 1.148e-05
 Residual              9.288e-02 3.048e-01
Number of obs: 852, groups:  subject, 71; token_set, 24; list, 2

Fixed effects:
                      Estimate Std. Error       df t value Pr(>|t|)    
(Intercept)            0.99723    0.03554 70.75609  28.056  < 2e-16 ***
groupHS               -0.11226    0.04723 67.77282  -2.377   0.0203 *  
groupSB                0.04257    0.05227 67.77205   0.814   0.4182    
conditionEN-GJT-R-RES -0.27753    0.03099 21.38884  -8.955  1.1e-08 ***
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Correlation of Fixed Effects:
            (Intr) gropHS gropSB
groupHS     -0.531              
groupSB     -0.480  0.361       
cEN-GJT-R-R -0.436  0.000  0.000
optimizer (nloptwrap) convergence code: 0 (OK)
boundary (singular) fit: see ?isSingular